In August of 2015, AAS Nova launched as a new service provided by the AAS journals. Today, five years later, we’re officially celebrating the milestone of the 1,000th Highlight post published on the site.
Beyond functioning as a news service, AAS Nova acts as an archive of astronomy research — which provides us with an interesting opportunity to explore how our understanding of the universe has developed.
Today we’re taking a moment to look back at a tiny sample of the new discoveries and ideas published across different corridors in the AAS journals and highlighted on AAS Nova over the past half-decade.
The faint object in the center of this image is NGC 1052-DF2, an ultra-diffuse galaxy at the center of a scientific debate about dark matter. [NASA/ESA/P. van Dokkum (Yale University)]
We’ve also continued to make progress toward resolving a number of long-standing debates, such as the question of why we don’t see as many small satellite galaxies as predicted (the “missing satellite problem”), or why our two methods of measuring the Hubble constant — a number that describes the rate of expansion of the universe — come up with different results.
Simulated image of two merging black holes, viewed face-on. LIGO announced the detection of ten of these events from its first two observing runs. [SXS Lensing]
High-Energy Phenomena and Fundamental Physics
One of the biggest headlines in the past five years was the first detection of gravitational waves from a merging pair of black holes. Since this discovery, the Laser Interferometer Gravitational-wave Observatory (LIGO) and its European counterpart, Virgo, have detected more than a dozen mergers of compact objects, and observatories across the world have searched for — and found! — electromagnetic counterparts to these collisions. Theoretical models of compact binary formation and evolution have also advanced in leaps and bounds as we’ve learned more.
Continuing the theme of “cool new observations of black holes”, the Event Horizon Telescope presented its view of M87 last year, opening a window onto what’s happening in the innermost regions around supermassive black holes. And we’ve amassed dozens of observations of black holes tearing apart passing stars in tidal disruption events, improving our models of this destruction in the process.
But outbursts from black holes aren’t the only transient phenomena flashing through our skies. The past few years have dramatically advanced our understanding of fast radio bursts, sudden, brief bursts of radio emission that originate from outside our galaxy. We now suspect these flashes might be related to high-energy phenomena, like the birth or evolution of distant magnetars.
This ALMA image of the protoplanetary disk surrounding the star HL Tauri reveals the detailed substructure of the disk, including gaps that may have been cleared by planets. [ALMA (ESO/NAOJ/NRAO)]
Interstellar Matter and the Local Universe
One of the biggest new players in the study of gas and dust in the local universe is the Atacama Large Millimeter/submillimeter Array (ALMA), which announced new results from its first long-baseline, high-resolution campaign around the time that AAS Nova first launched. Since then, ALMA has continued to produce spectacular observations — the array is mentioned in 82 of the 1,000 Highlights currently posted on AAS Nova, indicating the transformative nature of its observations.
As we peer deeper into interstellar clouds, we’ve also discovered a number of new molecules in the gas and dust of the universe, broadening our interstellar census and helping us to better understand our origins. Additionally, we’ve made significant advances in understanding the structure of magnetic fields in dense interstellar clouds and unraveling the role that they play in star formation.
Artist’s illustration of the Breakthrough Starshot Initiative, a plan to send a fleet of tiny spacecraft to Alpha Centauri. [Breakthrough Initiatives]
Laboratory Astrophysics, Instrumentation, and Software
While the most headline-grabbing astronomy is often major detections and observations, more attention has started to come to the important underlying work of exploring astrophysical phenomena in the lab — from the construction of white dwarf photospheres to the formation of dust grains under conditions mimicking the cold vacuum of space — and developing new and increasingly advanced instrumentation and software.
Human-made objects in space continue to both inspire and trigger debate. Recent developments include the Breakthrough Starshot Initiative to send a fleet of centimeter-sized spacecraft to the nearest star system, as well as the influx of satellites in low-Earth orbit and the impact this has on astronomy.
This composite image with enhanced colors shows New Horizons observations of Pluto (foreground) and Charon (background). [NASA/JHUAPL/SwRI]
On the small-body front, the New Horizons spacecraft flew by Pluto just before AAS Nova launched, and it then followed up with an up-close look at asteroid MU 69. Multiple interstellar asteroids have recently been observed as they pass through our solar system, and missions are underway to actually land on asteroids and return samples to Earth.
Artist’s illustration of the Parker Solar Probe. A special ApJS issue features around 50 articles detailing early results from this mission. [NASA/Johns Hopkins APL/Steve Gribben]
The Sun and the Heliosphere
In solar physics, we’ve continued to make steady progress toward solving major mysteries of our Sun, like how particles are accelerated in energetic solar flares, and why the outer solar corona is so much hotter than the layers of the Sun’s atmosphere that lie below it (the so-called coronal heating problem). We’re also gaining a better understanding of our broader solar system as the Voyager satellites and IBEX explore the heliosphere.
In addition to the large assortment of Sun-observing telescopes already on the job, we’re still finding new ways to explore our nearest star — from hard X-ray images to balloon-borne ultraviolet observations. An especially unique view is now coming from the Parker Solar Probe, a spacecraft that recently arrived at the Sun and is already producing results. This probe will continue to plunge ever closer to the Sun’s surface over the next five years.
Artist’s illustration of one of the most massive star clusters within the Milky Way. The center of the cluster contains 14 red supergiant stars. [NASA, ESA and A. Schaller (for STScI)]
A huge astronomical milestone was achieved with Gaia’s first and second data releases, which map the positions, parallaxes, and proper motions for more than a billion stars and have enabled a wealth of studies of our surrounding galaxy.
There are, of course, many more astronomical successes from the past half-decade than could be summarized in a short post here. Even so, this look back on the past five years of astronomy provides a clear sense of the remarkable advances we’ve made in a relatively short time.
It should be noted that our advances don’t negate the challenges that our field still faces — we have plenty of problems to address, like racial diversity, equity, and inclusion in astronomy. Nonetheless, as we look both inward and outward, we’re making steady progress toward understanding the universe around us and our role in it.
At AAS Nova, we’ve loved reporting on all that’s happened in astronomy over the past five years. We’re excited to see what the next five bring!
Editor’s Note: This week we’re at the 236th AAS Meeting, being conducted virtually for the first time! Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume the week of June 8th.
Solar Physics Division (SPD) Hale Prize Lecture: From Jets to Superflares: Extraordinary Activity of Magnetized Plasmas in the Universe (by Abby Waggoner)
The last day of AAS 236 started off with the Solar Physics Division Hale Prize Lecture by Kazunari Shibata from Kyoto University. Dr. Shibata was awarded the Hale prize for his years of research on magnetized solar and astrophysical plasma and the discovery of solar jets. Dr. Shibata is the first scientist from Japan to receive the Hale prize, which is the most prestigious award in solar physics.
Dr. Shibata didn’t always study solar physics. During his graduate studies (1973–1977) he sought to solve the “biggest puzzle in astrophysics”: the jets produced by active galactic nuclei (AGN). A series of jets were discovered in the 1960s, but the physics behind them was unknown at the time. AGN are difficult to observe directly, as they are billions of light-years away from Earth, so Dr. Shibata approached the problem from the theory side by studying magnetohydrodynamic (MHD) plasma. When the first protostellar jets were discovered, Dr. Shibata noticed that the morphologies of protostellar jets and AGN jets were similar, thus indicating that the jets were likely driven by the same physics.
At this point in time, scientists understood that jets in AGN originated from the transfer of kinetic energy produced by accretion, but the process by which the gravitational energy is converted to kinetic energy was still unknown. Dr. Shibata believed that the magnetic fields on the Sun were the key to understanding this, and he was right! He noticed that the spinning jets on the Sun could be related to the twist of a magnetic field.
This relation was confirmed when simultaneous observations in H-alpha and X-ray light were done on a single flare. Solar flare production by magnetic reconnection became known as the standard model. Dr. Shibata was able to connect the standard model to jets produced by AGN. Convection and rotation in the Sun (stellar dynamo) allow for the magnetic reconnection of magnetic field lines on the Sun, while accretion and rotation of the accretion disk around a black hole enables magnetic reconnection in AGN.
In the 1960s, the standard flare model was developed. Below the prominence, we have antiparallel lines that release magnetic energy. pic.twitter.com/yx4TbkrM1T
Dr. Shibata concluded his talk by discussing statistics done on the frequency of solar flares and the significance of “super flares.” He found that a super flare (energy range > 1033 erg, which is a lot of energy) could be produced by the Sun once every ~10,000 years. While we’ve never observed a super flare (luckily), he commented that a super flare could possibly be related to the origin and evolution to life on Earth.
(Conclusions continued) -"Extreme activity (such as superflares) on the Sun may have been related to the origin and evolution of life on Earth, whereas it would be extremely dangerous for our civilization in the future."
Press Conference: Mysteries of the Milky Way (by Haley Wahl)
Today’s first press conference follows on the heels of yesterday’s conference on the galactic center, and focuses on the broader picture of things.
The first speaker today was Dhanesh Krishnarao, a graduate student at the University of Wisconsin, Madison, speaking on the Fermi bubbles, which are massive lobes that expand out from the center of the galaxy. It’s known that these bubbles absorb light, but Krishnarao and his team discovered that they actually emit light too, and this was all seen by the Wisconsin H-Alpha Mapper, or WHAM! By measuring the optical emission and combining it with the UV absorption data, they were able to conclude that the Fermi bubbles have a high density and pressure. Press release
First discovery of optical light coming from Fermi Bubbles, paper on the ArXiv yesterday (arXiv:2006.00010)! Here's an artist's impression of the bubbles #AAS236pic.twitter.com/JOZVEwHEe9
The next speaker was Dr. Smita Mathur from Ohio State University to discuss a new discovery in the circumgalactic medium of the Milky Way. Before this work, the circumgalactic medium was thought to be mostly warm at temperatures around one million Kelvin. However, Mathur’s team discovered a hot component that’s around ten times as hot. No theory has ever predicted this!
How ubiquitous is that hot component of the circumgalactic medium? Dr.Anjali Gupta from Columbus State Community College, the third speaker of the press conference, explained! Using the Suzaku and Chandra telescopes, the team, led mostly by undergrad student Joshua Kingsbury, found the component in three out of the four sightlines they looked at. This hints at the fact that this hot component of the circumgalactic medium could be present in every direction, but more observations are needed. How can this hot component be explained? It’s possible that it could be related to feedback, from active galactic nuclei and/or from stars (star formation and supernovae)! Press release
The location of the Ursa Major Arc relative to the Big Dipper. [Stellarium.org/A]
The last speaker of the press conference was Dr. Robert Benjamin from the University of Wisconsin, Whitewater, who spoke on a surprising result in a familiar sight in the nighttime sky. Benjamin and his team discovered a thin UV arc shock front whose length in the sky is 30° — that’s 60x the apparent size of the full Moon! If the arc were extended, it would make an enormous circle on the sky with a radius that’s also 30° in size. They believe the arc to be about ~100,000 years old and >600 light-years away and possibly caused by a supernova; if this is the case, it would be the largest supernova remnant in the sky. Press release
Plenary Lecture: Our Dynamic Solar Neighborhood (by Luna Zagorac)
Jacqueline Faherty (American Museum of Natural History) studies our solar neighborhood (20–500 pc from the Sun) because it lets us investigate faint sources in more detail, including brown dwarfs. One important question we can begin to answer in the solar neighborhood is where the high-mass limit of planet formation ends and the low-mass limit of star formation begins. To illustrate what the stellar neighborhood looks like, Dr. Faherty took us on a virtual flight using the OpenSpace software, illustrating the advancement in mapping and astrometry from the Hipparcos data set to Gaia DR2, which mapped more than 1.3 billion sources. Gaia is an optical survey and, as such, is not very sensitive to faint, cold sources like brown dwarfs. When Gaia data was combined with ground-based measurements, however, 5,400 sources were extracted from the sample of Gaia objects within 20 parsecs of the Sun. These sources could then be arranged on a color-magnitude diagram (known as an HR diagram), with brown dwarfs clustering in the lower-left part of the diagram.
Here's these satellites plotted on a color magnitude diagram (an HR diagram)! White dwarfs in the lower left corner. pic.twitter.com/3snO7H8JNn
The scatter and differentiations in the diagram give insight into atmospheric characteristics of the colder objects represented. The coldest objects at the end of the spectral sequence, named Y dwarfs, are difficult to find because they’re not very luminous. Their temperatures are around 400 K, and their masses are estimated at ~20 Jupiter masses. These are the very markers of the transition between the bottom of the star formation process to the top of the planet formation process. The best way of identifying these objects has been through citizen science projects — the human eyes are the best recourse we have for identifying brown dwarfs!
Adding the discoveries from the Backyard Worlds citizen science project to the Gaia DR2 20 parsec sample will allow further constraining of brown dwarfs’ mass function. Citizen scientists are also helping to identify co-moving companions to stars, since their mass and separation distribution reveals more information about their formation. This is important because age can determine the mass of the object: “In determining co-moving structures, we can measure their ages and we can use those to do a deeper dive to systems within them,” noted Dr. Faherty. This project is being led by her postdoc, Dr. Daniella Bardalez Gagliuffi.
Furthermore, there are objects in the Tucana-Horologium Association that are in systems where a companion has been discovered right on the mass boundary between planet and brown dwarf formation. These companions resemble Jupiter and have thick clouds, and Dr. Faherty wants to study how their light is changing. To find more of these systems, her former student Dr. Eileen Gonzales is developing BREWSTER, a retrieval code optimized for brown dwarfs, but adaptable to planets as well.
"These companions are at a temperature that's kind of crazy." Here's an example. They look a lot like Jupiter and have thick clouds. We want to look at how their light is changing. pic.twitter.com/9Oz4W4pLwj
These data sets have allowed us to better visualize low-luminosity object distributions in the sky, and Dr. Faherty hopes this can be turned into planetarium presentations. She concludes that the multi-dimensional nature of stellar catalogs is highly complemented by visualization tools and that the James Webb Space Telescope will be critical in further characterizing these low-luminosity objects.
OSTP Town Hall with White House Science Advisor Kelvin Droegemeier (by Tarini Konchady)
Note: In the recording of this session, Dr. Droegemeier’s audio for the Q&A was lost. This writeup covers everything that was said before the Q&A.
The main speaker at the Office of Science and Technology Policy (OSTP) town hall was Director Kelvin Droegemeier. Droegemeier’s scientific background is in meteorology; in 1985 he joined the University of Oklahoma as an assistant professor and has remained at that institution to this day (he has taken a leave of absence to serve as OSTP director). Droegemeier has a long career in federal policy as well, notably serving on the National Science Board from 2004 to 2016. Aside from being OSTP director, Droegemeier is also the Acting Director of the National Science Foundation. He will stay in this role till the Senate confirms the president’s nominee — Sethuraman Panchanathan — for the job.
The Office of Science and Technology Policy (OSTP) Town Hall happening now! Today's speaker is Dr. Kelvin Droegemeier, OSTP Director and Acting NSF Director.#aas236
Droegemeier emphasized that his experience as a college professor has informed his work in the federal government. He spoke about two particular OSTP efforts relevant to the AAS: one, helping colleges and universities with “reopening and reinvigorating” after the pandemic, and two, enabling research that would benefit the country.
To the first point, Droegemeier listed various meetings that have been happening between university leadership and federal bodies (including the Vice President and the National Science and Technology Council) as well as guidance issued by the government. He used these examples to emphasize that the government is apparently willing to give institutions leeway if it will allow smoother operations during the pandemic.
Droegemeier briefly switched gears to share the most recent status of astronomical facilities per James Ulvestad, Chief Officer for Research Facilities. Nothing differed significantly from the update given at the NSF town hall yesterday, though Droegemeier mentioned that the parking lot of the National Solar Observatory’s Boulder facility had been used for COVID-19 drive-through testing till recently. Construction on the dome and telescope mount of the Vera Rubin Observatory are unlikely to resume until September or October.
Droegemeier then pivoted back to OSTP business with an update on the Joint Committee of Research and Enterprise (JCORE), which was formed a little over a year ago. The four areas JCORE focuses on are research security, research integrity and robustness, research administrative workload, and safe and inclusive research environments. Droegemeier emphasized that the committee was continuing to work through the pandemic, especially the research security subcommittee.
In the same vein, Droegemeier spoke about how he had been going around the country to talk to faculty, students, and researchers about research security prior to the pandemic. Lisa Nichols, the OSTP Assistant Director of Academic Engagement, was also part of this effort.
Around this time of year, the OSTP issues an R&D guidance memo to federal agencies, setting priorities for the next fiscal year. The memo is purely guidance and does not contain any funding. Two of the key topics of last year’s memo was American security and “industries of the future” — technologies like artificial intelligence and 5G connectivity.
National High Performance Computing User Facilities Town Hall (by Sanjana Curtis)
The National High Performance Computing (HPC) User Facilities town hall was kicked off by Dr. Richard Gerber (NERSC) who introduced the goals of the town hall: inform the community about HPC and new directions in HPC, discuss opportunities for using HPC to advance astronomy research, communicate what is available at National HPC centers, and gather feedback from the community about their questions, needs and challenges. He also introduced the other presenters from major HPC facilities around the US: Niall Gaffney (TACC, UT Austin), Michael Norman (SDSC, UCSD), Jini Ramprakash (ALCF, Argonne National Lab), Bronson Messer (OLCF, Oak Ridge National Lab), and Bill Kramer (NCSA/Blue Waters, UIUC).
Dr. Gerber defined HPC as computing and analysis for science at a scale beyond what is available locally, for example, at a university. HPC centers have unique resources, including supercomputers, big data systems, wide-area networking for moving data quickly, and ecosystems that are designed for science (for, e.g.: optimized software for simulations, analytics, artificial intelligence and deep learning). These centers also offer lots of support and expertise, since they are staffed by people who are experts in HPC, many of whom have a science background. This helps bridge the gap between the domains of science and computing.
The IBM Blue Gene/P supercomputer “Intrepid”. [Argonne National Laboratory]
The traditional picture of a supercomputer is a system consisting of hundreds of thousands of the world’s fastest processors, coupled together by very high speed custom networks. Typically, they have a large scratch disk (~petabytes) optimized for reading and writing large chunks of data. These machines were originally designed to have all their compute nodes tightly coupled, where each node needs to know what the other nodes are doing, mainly to solve partial differential equations using linear algebra — they are really good at matrix multiplications! Users interact with supercomputers via SSH and command line, and submit their jobs to a scheduler or queue system for execution.
However, the HPC landscape is now changing, and rather abruptly! Single-thread processor performance growth that used to be exponential (Moore’s law-like) has stalled. Instead, we have to rely on parallelism and accelerators for increase in performance. Demand for data analysis is expanding, both from experimental and observational facilities, and large collaborative teams have become the norm. We are also witnessing the rise of artificial intelligence (AI), machine learning, and other emerging technologies with new needs.
So what’s next for HPC? According to Dr. Gerber, HPC will continue to advance the limits of computation and analysis. We will see data-intensive science and simulation science merging together, and large scale analysis of experimental and observational data moving to HPC. Since AI and deep learning are here to stay, HPC centers will have to accommodate this demand. Finally, supporting large collaborations will require enabling tools, such as tools for user authentication and data management.
Dr. Niall Gaffney (TACC) was up next, speaking about Astronomy and Advanced Computing in the 21st Century. He started out by mentioning the three pillars of modern computational science: simulation, analytics and machine learning/AI. Astronomy and computing are old friends and there exists a long list of very impressive simulations, such as the Renaissance Simulation, the SciDAC Terascale Supernova Initiative, black hole merger simulations for LIGO, and more! These large simulations are what people typically associate with supercomputing centers. However, there was a shift in this paradigm whenSDSS came online and showed astronomy the power of large-scale data and compute resources. The notion of a data center where you could go to run your analysis, without having to download huge quantities of data, was a big change. Now, there is an explosion of AI and machine learning methods, required by facilities like the Vera Rubin Observatory that will generate large amounts of data at very high rates. Astronomy has always been at the forefront of computational science and will continue to drive the field forward.
Not just the three pillars of astronomy, but many observational sciences! Astronomy has been key in pushing this forward. We've always had big data (physics of building a CPU = building a CCD!) #AAS236pic.twitter.com/EU6t7YG5Ku
One benefit of working at an HPC center, according to Dr. Gaffney, is that they are not limited to astronomy. As an example, he cited the use of machine learning to look for anomalies in traffic flows, which is similar to looking for anomalies in data streams coming from telescopes like the LSST! He then discussed the specifications of the Frontera system at TACC, currently the 5th fastest supercomputer in the world and the fastest on any university campus. He concluded by telling us that HPC does not look like it used to! There is a rise of GUI and convenient environments, including Project Jupyter notebooks.
The next speaker was Dr. Michael Norman (SDSC) who talked about their existing system Comet and their plans to deploy a new machine, called Expanse, this summer. Both systems are designed to support the “long tail of science” — small to medium sized HPC batch jobs. Large, full-scale simulations are better done at facilities like TACC. The barrier to entry is low and trial allocations are available within 24 hours! The uniqueness of their new machine, Expanse, comes from its integration with things outside the machine room, such as the cloud and the open science grid. It will support composable systems, containerized computing and cloud bursting. Using the bright cluster manager, the machine will simultaneously have a slurm cluster running the usual batch jobs, and a kubernetes cluster running containerized software!
Soon, will have both Slurm jobs running continuously and Kubernetes jobs running containerized jobs! The divide will be set by user demand #AAS236pic.twitter.com/IdTt9X0fqN
Next, Dr. Gerber highlighted some of the machines at NERSC, including the upcoming Perlmutter, and gave us a breakdown of how their computing time is allotted: 80% DOE Mission Science, 10% Competitive awards run by DOE, 10% Director’s Discretionary Strategic awards.
He was followed by Dr. Jini Ramprakash (ALCF) who described the supercomputing resources available at ALCF: the supercomputer Theta, a smaller system called Iota, the Cooley visualization cluster, and disk and tape storage capabilities. Their big push right now is Aurora, an exascale CPU/GPU machine that should be ready by 2021. Awards exist at different levels, including for getting started (Director’s Discretionary), major awards (INCITE, ALCC), and Targeted Projects (ADSP, ESP).
Dr. Bronson Messer (OLCF) was next. He started out by describing the infrastructure at OLCF — including impressive numbers like their 40 MW power consumption and 6,600 tons of chilled water needed for cooling! Their supercomputer, Summit, is currently the top supercomputer in the world and they have a host of smaller support machines as well. In 2021, they plan to deliver their own exascale machine called Frontier. The big change will be moving from Nvidia GPUs in Summit to AMD GPUs in Frontier. Oak Ridge has been using CPU/GPU hybrid methods for a long time, and will continue to do so. There are three primary user programs for access and allocations are split as 20% Director’s Discretionary, 20% ASCR Leadership Computing Challenge, and 60% INCITE. The allocation application for the Director’s Discretionary program can be found on their website (https://www.olcf.ornl.gov/) and has a one week turnaround!
Wrapping up the town hall was Dr. Bill Kramer (NCSA) discussing Illinois, NCSA and Blue Waters, and the evolution of HPC. The NCSA is the first NSF supercomputing center andBlue Waters is the first NSF Leadership System. It is the largest system Cray has ever built and is also a hybrid containing both CPUs and GPUs. In addition to Blue Waters, the NCSA computational and data resources include Delta (award just announced, details to come), Deep Learning MRI Award (HAL and NANO clusters), iForge (mostly industrial and recharge use) and XSEDE services. Blue Waters has so far provided more than 9.3 billion core-hour equivalents to astronomy, which accounts for over 27% of its total time. Dr. Kramer concluded by reminding us that integrated facilities for modeling, observation/experiment, and machine learning/AI are the future — multipurpose shared facilities are where we are going!
Press Conference: Sweet & Sour on Satellites (by Amber Hornsby)
For the final press conference of the summer AAS meeting, we hear all about satellites — both the good and the bad.
First up, @AstroRach tells us about a hunt for the first stars that were born in the universe. Observations from Hubble suggest they may have formed even earlier than we previously thought — within the first 500 million years after the Big Bang! #AAS236pic.twitter.com/OgHpP11OPz
Kicking off, we first hear from Dr. Rachana Bhatawdekar (ESA/ESTEC) with an exciting update on the hunt for stars in the early universe — they possibly formed much sooner than previously thought. As part of the Hubble Frontier Fields programme, the Hubble Space Telescope (HST) produced some of the deepest observations of galaxy clusters ever. Galaxies located behind the cluster are magnified, thanks to gravitational lensing, which enables the detection of galaxies 10 to 100 times fainter than any previously observed. Through careful subtraction of bright foreground galaxies, Bhatawdekar and collaborators were able to detect galaxies with lower masses than previously seen by Hubble, and at a time when the universe was less than a billion years old. The team believes that these galaxies are the most likely candidates driving the reionization of the universe — the process by which the neutral intergalactic medium was ionised by the first stars and galaxies. Press release
Next up, we hear from Nobel Laureate Prof. John Mather (NASA Goddard Space Flight Center) on hybrid ground/space telescopes and the exciting possibilities of improved observations through artificial stars and antennas in space. Many telescopes use lasers to create an artificial star in the sky, which allows them to track the ever-changing atmosphere, and correct for this effect using adaptive optics. However, Mather and the team are proposing to instead beam a star back down from space to Earth, enabling ground-based telescopes to beat the resolution of space-based telescopes. Another hybrid ground/space telescope suggestion includes dramatically improving the abilities of the Event Horizon Telescope via orbiting antennas.
Moving on from the sweet, Prof. Patrick Seitzer (University of Michigan) introduces the sour theme of the second half of the press conference: large constellations of orbiting satellites and their impact on astronomy. Trails created by satellites saturate an instrument’s detectors and often create so-called ghost images which were briefly mentioned during yesterday’s plenary session on satellite mega constellations. With companies like OneWeb hoping to put more than almost 50,000 satellites in orbit, the future is looking a bit bleak for astronomy, with over 500 satellites contaminating the summer sky every hour, throughout the available observing hours, for the planned Vera Rubin Observatory (VRO). The only positive throughout this is the SpaceX starlink satellites, due to launch this evening, are trialing sun shades to block antennas from reflecting sunlight.
But how do we live with large constellations of satellites? Prof. James Lowenthal (Smith College) discusses the worst case scenario — the impact of satellites on VRO images. With current satellite plans, most of the planned VRO observations will be impossible to schedule, even if we try to avoid satellites. This represents a major collision of technologies between mega constellations and the desire of astronomers to do large-scale survey astronomy. The AAS is seeking out ways to reduce their impact, through surveys of the astronomy community and discussions with both SpaceX and OneWeb. But these two companies are not the only players in the field — so it looks like mega constellations are here to stay, and we will have to work with their operators to target “zero impact” on astronomical observations.
Gone with the Galactic Wind: How Feedback from Massive Stars and Supernovae Shapes Galaxy Evolution (by Haley Wahl)
Our very last plenary of the meeting was given by Dr. Christy Tremonti from the University of Wisconsin, Madison. Tremonti took us on a trip through the process of stellar feedback, showing us what causes it and how it affects star formation.
Feedback is the process by which objects return energy and matter into their surroundings (for example, black holes spewing out jets into the surrounding interstellar medium). In the context of galaxies, feedback is very important because it helps slow down star formation. Without feedback, star formation would progress much more quickly, resulting in galaxies today with very different shapes than what we observe. Feedback influences star formation rates, stellar masses, galactic morphology, and the chemistry of the interstellar medium and circumgalactic medium.
Galactic feedback comes from five major sources. The first of those is supernovae; when massive stars explode, they release an enormous amount of energy into the surrounding interstellar medium, and they create pressurized bubbles of ejected material that expand and sweep up ambient gas. The second is stellar winds, which contribute as much energy and momentum as supernovae, but begin immediately, whereas supernovae effects are delayed by a few million years. The third is radiation pressure on dust grains. When ultraviolet radiation radiation hits a dust grain, it is reradiated in the infrared; these infrared photons carry momentum and in order to conserve it, the dust grains must move, causing the radiation pressure. This can be a significant contributor to the feedback in the center of very dense, dusty galaxies. Another source is photoionization, a process where ionizing ultraviolet photons heat the surrounding gas. The final source of feedback is cosmic rays. Around 10% of a supernova’s energy is thought to be in cosmic rays, and these rays scatter off magnetic homogeneities in the ISM, transferring the cosmic ray momentum to the gas. All of these processes can contribute to the feedback process on different temporal and spatial scales.
The process of feedback creates a cool phenomenon called a “galactic fountain.” Galactic fountains are formed when star formation surface densities are low and isolated superbubbles break out of the disk. When star formation surface densities are high, these superbubbles begin to overlap and they can more efficiently drive centralized outflows. In the local universe, winds are primarily found in starburst galaxies like M82. This galaxy is very close, which allows us to study it in detail.
M82 is a good galaxy to study for galactic winds. Starting with x-rays. Hard x-rays show key feedback processes (blue) #aas236pic.twitter.com/dqtmtZO0Qs
In the future, through multi-wavelength studies and with tools like the Athena X-Ray Observatory (planned for 2030), astronomers hope to make progress relating simulations and observations in order to learn more about the processes of feedback.
Editor’s Note: This week we’re at the 236th AAS Meeting, being conducted virtually for the first time! Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume the week of June 8th.
AAS Publishing Exclusive: A Discussion with the arXiv Executive Director (by Alex Pizzuto)
Day 2 of the meeting started strong, featuring a discussion with arXiv Executive Director Eleonora Presani, who detailed the current status and future outlook of the open access archive service many of us know and love. Not only is Presani new to the role of executive director, but the role itself is only two months old, marking a step towards engaging with the scientific community more efficiently and productively. As someone equipped with both a PhD in astroparticle physics and more than 6 years of experience from a career in scientific publishing, Presani is extremely qualified to help execute the vision of arXiv.
Presani began her presentation with her own mantra on the dissemination of scientific research: “knowledge only exists if it is accessible.” As an organization, Presani believes that arXiv functions as the “enablers” for the sharing of this knowledge, and seeks to make accessible environments like arXiv; those which are for researchers, by researchers. To get a sense of the sheer volume of knowledge that passes through the arXiv servers, Presani quizzed her audience, revealing some dumbfounding statistics about the quantity of preprints that have been submitted:
A few stats: -3,000: the amount of submissions arXiv receives per week -240,000: number of articles in astro-ph -200: the number of papers submitted to astro-ph per wee
The funding comes from 35% members, 12% gifts, and 53% funding [from institutions, societies like AAS, etc.].
The fact that about half of the funding for arXiv is from the community is a testament to the fact that arXiv exists to serve the community.
Although many organizations have been slowed to a halt by the tragic global pandemic, Presani assures us that arXiv is still working hard. Over the last few months, arXiv has rolled out user-driven classification, which alerts authors when they assign their papers to a category that disagrees with arXiv’s classification algorithm. They have also been executing operational stability drills and developing a COVID-19 moderation plan, to make sure that no matter what is going on in the world, scientists can stay connected through their research.
Looking more to the future, we were then told about arXiv’s 3-year strategic plan (picture below). This plan is broken down into three distinct user categories (readers, authors, moderators) and discusses how each of these users can benefit in three different areas (control, impact, and collaboration). In order to successfully execute this plan, however, arXiv requires our help and wants to hear from scientific communities like the AAS, in order to learn what researchers believe are the highest impact deliverables.
There are also some specific tasks that the arXiv team is focusing on over the next 18 months. These include distributing some of their classification data to Kaggle, allowing users to contribute to classification algorithms. Additionally, arXiv will be rolling out an update to TeXLive2020 and is actively working on improving their user disambiguation techniques.
Focusing arXiv’s resources to decide which of these goals is completed first is no simple task. Presani highlighted how challenging it is to balance all of the lofty goals of arXiv with their limited resources and discussed how no changes should be rolled out until they are up to arXiv’s high standards, noting that “arXiv was launched in 1991, and when it launched, it was an extremely cutting-edge product and it stayed the same for 30 years. It’s important to find the right balance between being quick and keeping the high quality of the work.”
Interested in helping arXiv execute their vision? There are a variety of ways to contribute. Start by joining arXiv’s user testing or read their blog and news/announcements. They are also looking for volunteers to help with developing a better moderator workflow, and they are soliciting applications for volunteers (if interested, you can send your CV and a motivation letter to moderation@arxiv.org). Best of all, continue to use the arXiv and engage in discussion with the administrators about what your perfect arXiv would look like in the future.
Laboratory Astrophysics Division (LAD) Plenary Lecture: The Crucial Interplay of Laboratory Experiments, Observations and Theory to Unveil our Astrochemical Origins (by Abby Waggoner)
Our first plenary talk of the day was given by Paola Caselli from the Max-Planck-Institute for Extraterrestrial Physics. Dr. Caselli discussed how laboratory experiments, observations, and theory can be used to better understand the origins of biologically related molecules in space. Life as we know it is made up of amino acids, so many astrochemists seek to understand the origin of amino acids in astronomical environments. Currently, over 200 amino acids have been detected in meteorites, and amino acid precursors have been detected in molecular clouds beyond our solar system.
Our molecules and their building blocks tell us the history of living beings! #AAS236
Known molecules in the solar system are "prebiotic," and often detected by knowing their frequencies really well form lab experiments! pic.twitter.com/3b3QfI6BpF
To truly begin understanding our astrochemical origins, we begin in a pre-stellar core. Pre-stellar cores lead to the formation of a star and protoplanetary disk. These cores can reach temperatures as low as 6 K, which enables molecules to stick to grains and form an icy coat. 6 K is very cold, so we would expect all of the water in a prestellar core to be frozen out — but water vapor has been detected in these cold regions. These observations led to the question, how is water getting into the gas phase?
The answer was found using theory. High energy particles (typically protons) accelerated by supernovae and jets from stars, called cosmic rays, can penetrate the ice layers on dust grains. Cosmics rays excite atoms and molecules in the ice, resulting in the production of electrons that can essentially knock the ice into the gas phase and cause chemical reactions to occur. Theory has even shown that the presence of cosmic rays enables the production of complex organic molecules (COMs), such as methanol and other molecules that may eventually play a part in the formation of life.
Plasma physicist at Max Planck Alexei Ivlev is working on how cosmic rays affect ice composition (Shingledecker 2017, 2018), helping refine theories and predictions!
Interstellar ices also tell us a bit about the timeline on which molecules froze and were created. Typically, a hydrogen atom (H) is a single proton and electron, but a fraction of all hydrogen is made up of a proton and neutron, which we call deuterium (D). Deuterium fractionation, or the ratio of H to D, tells us the origins of molecules. For example, the Earth’s oceans have an H/D ratio ten times higher than the Sun’s, suggesting that water on Earth is older than the Sun and comes from meteorites or comets.
Deuterium fractionation and the formation of COMs in prestellar cores tell us that our chemical origins trace all the way back to molecular clouds. Dr. Cadelli’s talk emphasized that we must use laboratory experiments, theory, and observations in order to understand the chemical inheritance of our solar system. Molecules are everywhere, and we need to work together to understand them.
Press Conference: Galactic Center To & Fro (by Susanna Kohler)
This morning’s press conference explored the center of our galaxy, the Milky Way, “in every which way”, according to conference host and AAS Media Fellow Tarini Konchady.
Christopher Russell (Pontificia Universidad Católica de Chile) opened the session by introducing a new virtual reality app that allows the public to personally experience flying through the galactic center — both through frozen scenes and through 500 years of cosmic evolution, all built from a combination of observations and simulations. Already got a virtual reality setup? The new app, Galactic Center VR, is free through both Steam and Viveport. Have a gaming computer but no VR headset? Typical cost for a headset is a few hundred dollars — which means you can travel to the center of our galaxy for the same price as a plane ticket to travel across the country! Check out a video clip of the VR experience below. Press release
We live in a galaxy where gravity determines how most things move. But could there be regions where the dynamics are instead governed by something else — like magnetic fields? Joan Schmelz (Universities Space Research Association) presents new observations from our favorite flying infrared telescope, the Stratospheric Observatory for Infrared Astronomy (SOFIA), which allow us to map out the streamlines of plasma moving in the central ~15 light-years of our galaxy. These observations show that, despite the strength of the supermassive black hole’s gravity, the plasma motion in the region around Sgr A* is governed primarily by magnetic fields. Results like this one from SOFIA continue to help us reshape our understanding of processes in our galaxy. Press release
A look at our galaxy’s center in radio wavelengths reveals some curious features: long, thin filaments that span distances of up to hundreds of light-years, but are only a fraction of a light-year in width. What are these odd structures, and why do we see them? Shuo Zhang (Bard College) presents X-ray observations of several newly detected filaments that help us to answer this latter question. The new detections lead Zhang and collaborators to hypothesize that the filaments are lighting up in radio and X-rays as they’re bombarded by energetic particles accelerated in the galaxy’s core — possibly by the black hole Sgr A* itself. Press release
The galactic center contains mysterious filaments seen at radio and X-ray wavelengths. [Slide from Zhang; Image from MeerKAT/SARAO]
Closing out the session, Andrew Fox (Space Telescope Science Institute) presents an exciting possibility: though Sgr A* is quiet now, our supermassive black hole may not always have been so peaceful. Fox proposes that, just 1 to 4 million years ago, the galaxy’s center produced an enormous flash known as a Seyfert flare. This flash of light would have made the night sky look dramatically different for our ancestors millions of years ago! Fox shows that this theory is supported not only by the creation timeline for the Fermi Bubbles (a topic we’ll be touching on in greater detail in tomorrow morning’s press briefing), but also by evidence of photoionization in the matter that makes up the Magellanic Stream, a stream of gas that trails the Large Magellanic Cloud and may have been in the line of fire when cones of ionizing ultraviolet radiation erupted from the galactic center during the flash. Press release
An intense flash from the galactic center a 1–4 million years ago may have provided our ancestors with a very different night sky. [Gerald Cecil (UNC)]
Plenary Lecture: Satellite Mega-Constellations and the Night Sky: OIR Visibility, Impacts, and Policy; and An Introduction to the RF Spectrum Regulations (by Luna Zagorac)
The first half of this midday plenary was given by Dr. Sandra Cruz-Pol, a Program Leader at the National Science Foundation. Dr. Cruz-Pol underscored the importance of radio frequency (RF) signal management by explaining that if our eyes were able to see all the radio signals that surround us, we couldn’t see farther than a few meters. Furthermore, without regulation of RF channels, all of our communication devices would be rendered unusable due to interference — including cell phones, satellite TV, GPS, hurricane tracking, and more! After all, the RF spectrum is a limited resource, and radio regulations are constantly changing to keep up with new technologies.
Radio regulations exist at both the international and national levels. Since satellites regularly cross borders, their feeds need to be regulated internationally through the International Telecommunication Union, a UN agency. The ITU splits the world into three regions (with the Americas constituting Region 2), and holds the World Radiocommunications Conference (WRC) every 3–4 years in Geneva. The conference lasts for 4 weeks, and produces both radio regulations via international treaty, which all signatories must abide by, and recommendations, which are typically not mandatory. Nationally, federal assignments are handled by the National Telecommunications Information Administration (NTIA), and non-federal cases are handled by the Federal Communications Commission (FCC). In order for the FCC to adopt a proposal to change RF spectrum regulations in the US, a three-step process is necessary.
The NTIA also publishes the Frequency Allocation Table (FAT), which shows the signals at each frequency band, including primary allocations in capital letters and secondary allocations in lowercase. Primary allocations grant specific services priority in using the allocated frequency band; if there is more than one, they have equal rights, and have a right to be protected. Secondary allocations involve services that are allocated the same band as primary allocations, but must act to protect and accept interference from primary allocations.
In order to keep up with federal and international regulations, many organizations have Spectrum Managers — including Boeing, Nokia, Google, NASA, NOAA, the Navy, and more. NSF has two Spectrum Managers, who can be contacted for assistance with frequency assignments or questions at ESM@nsf.gov. Spectrum Managers also have to keep up with the many acronyms of various RF services — such as RAS (radio-astronomy service), SRS (space research satellite service, including near-Earth), ISS (inter-satellite service), and more.
Dr. Cruz-Pol closed by noting that RF allocation is a complicated topic on which she teaches an entire course, and so many details were left out of her presentations. She also provided listeners with an overview of free resources available online for those interested:
After that, Mary Elizabeth Moses Professor of Astronomy James Lowenthal of Smith College began his address with solidarity with those suffering from distress over recent events, especially the death of George Floyd and the longstanding harm of institutional racism and police brutality in the US. He then proceeded to show an image of a trail of StarLink satellites, stating: “My life as an astronomer changed early last year when I saw this for the first time.” The launch of StarLink satellites began in 2019, and a total of approximately 1,600 StarLink satellites are scheduled to be in the sky by the end of 2020. The satellites are launched into Low-Earth Orbit (LEO), starting at about 300 km and reaching their final altitude of about 550 km. They are relatively big satellites, about 3.5 by 8 meters long, and they are meant to provide fast broadband low-latency internet coverage worldwide.
The total number of objects in LEO is close to 20,000, consisting mostly of fragmentation debris, which is generated when larger objects collide and fragment into small pieces — intentionally or otherwise. However, most of these objects are not visible to telescopes and are far from visible to the naked eye. This is not true of StarLink satellites, which have elements that reflect sunlight to Earth and have a brightness magnitude less than 5, most noticeably around morning and evening twilight. The satellites have three phases of life — launch and orbit raise (1–6 weeks), operation (5–25 years), and de-orbit — all of which can impact observations, and different satellites might be in different phases concurrently. Modelling from the Vera Rubin Observatory (formerly LSST) showed that on the night of the summer solstice in Chile, 1–9 StarLink satellites would be visible to the observatory at twilight if orbitingat ~500 km. If the satellites were raised to 1,150 km altitude (still technically LEO), 10–25 satellites would be visible all night long.
The brightness of the satellites can completely saturate the CCDs of the VRO, leading to tracks of corrupted data. Furthermore, if they are bright enough, they can produce “ghost trails” that are impossible to correct for in the data, rendering more of the image unusable. With the current number of StarLink satellites, VRO can dodge some of these trails in its field of view, but as the numbers rise this will become impossible. Furthermore, some telescopes with wider fields of view are already unable to do this.
This is a major collision of technologies: the new advanced land-based telescopes and satellite mega-constellations. Dr. Lowenthal notes that, as described by Dr. Cruz-Pol, the protection of the radio sky has been a fortunate fact for decades; however there is no such protection for the optical/infrared sky. While the launch of a satellite requires permissions from many agencies, including the FCC, FAA, and ITU, it decidedly does not require permission from the AAS, the International Astronomical Union, or the International Dark-Sky Association. To suss out the impact of these mega-constellations, the AAS sent out a survey in December 2019 and got answers from all seven continents, including astronomers at observatories like VRO, Gemini, VLT, ZTF, APO, ATLAS, Las Campanas, and more. The answers for current impacts reported a wide range of 0–100% of science lost, with the majority expressing significant concerns, and in some cases significant costs. In the projection of 20,000 more bright satellites (compared to 1,584), 17/23 respondents noted that virtually all their science would be impacted, with 12/23 projecting critical failure of the facility.
The AAS has been in conversation with satellite operators (primarily SpaceX), and CEO Elon Musk has committed to reducing StarLink’s impact on science to zero. There have been several attempts to minimize brightness, including painting the satellites black (DarkSat), equipping them with visors to shield from sunlight (VisorSat), and re-orienting them so that the sunlight falls on the knife-edge of the satellite, minimizing reflection. However, other operators are planning to launch LEO satellites in the near future, prompted by a $20 billion subsidy from the FCC for such activities, and there is no guarantee that they will be as collaborative as SpaceX.
Finally, Dr. Lowenthall voiced his opinion, which is that astronomy is facing its most serious threat ever in LEO satellite mega-constellations. He further reflected on the impact of the sky to the human experience, including what the stars and the sky are worth; whose sky is it and who decides; what the value of exploring the cosmos is; and if there are viable alternatives to LEO satellite mega-constellations. Last, he emphasized that the impact of these constellations on the ecosystem is not known, but should be explored — for example, with respect to migratory birds using the stars to navigate. He encouraged astronomers to promote and lead such discussions internationally and with multiple stakeholders, and he then finished with a time-lapse from his own backyard in Massachusetts, asking attendees to spot the StarLink trails.
Dr. Lowenthal ends with this image taken from his home and asks us to to spot the starlink satellites… #AAS236pic.twitter.com/oOygnn2imG
National Science Foundation (NSF) Town Hall (by Tarini Konchady)
The National Science Foundation (NSF) town hall featured Ralph Gaume, Director of the Division of Astronomical Sciences (AST); Jim Neff, AST Deputy Division Director; and B. Ashley Zauderer, an AST Program Director whose programs include the Arecibo Observatory and Electromagnetic Spectrum Management.
Gaume’s presentation focused primarily on the impact of COVID-19 on AST and the NSF. A number of NSF-managed observatories have been operating through the pandemic, specifically the National Radio Astronomy Observatory facilities, Green Bank Observatory, Arecibo Observatory, the Global Oscillation Network Group, and Gemini North. The facilities currently idle are Gemini South, the Cerro Tololo Inter-American Observatory (CTIO), ALMA, and the Kitt Peak National Observatory (KPNO). Construction on the Vera Rubin Observatory (VRO) and the Daniel K. Inouye Solar Telescope (DKIST) has also paused. Many of the stalled facilities will require significant work to bring back online, with ALMA in particular posing an enormous challenge. The roadmaps for the next few years regarding VRO and DKIST will also have to be reworked.
The results of the Decadal Survey will also be presented later than anticipated, but the NSF transitioned very smoothly into teleworking right from March. Gaume also mentioned personnel changes in AST and the NSF as a whole. Most notable is the end of France Córdova’s term as NSF Director on March 31 this year. Her likely successor is Sethuram Panchanathan, who was nominated by the President in January. While Panchanathan’s nomination makes its way through Congress, Kelvin Droegemeier (who will be at an AAS 236 town hall tomorrow) has been serving as Acting NSF Director. Droegemeier is also Director of the Office of Science and Technology Policy, which advises the White House.
Gaume wrapped up by highlighting science from the NSF’s facilities, including the new NSF’s National Optical-Infrared Astronomy Research Laboratory — NOIRLab for short. NOIRLab was founded on October 1 last year and consists of all the NSF’s nighttime ground-based observatories in addition to the Community Science and Data Center. The rest of the science highlights can be found in the Twitter thread linked below:
The NSF's new telescope has taken the highest resolution ground or space-based image of the Sun ever taken by humans; resolution is a few tens of kilometers! pic.twitter.com/z7lChwnXEA
On the budget side, AST and the NSF are doing reasonably well. As usual, the President’s Budget Request for the fiscal year 2021 decreased NSF funding, but also as usual, Congress appropriated funds for the NSF at a level higher than the Request level. Legislature to watch includes the Securing American Leadership in Science and Technology Act, introduced by Republicans on the House Committee of Space, Science, and Technology, and the Endless Frontier Act, spearheaded by Senate Minority Leader Chuck Schumer. The latter would significantly change the operations of the NSF and other federal organizations.
Gaume then handed things off to Neff, who focused on the status of various AST grants. Neff emphasized that the grants and programs under AST were heavily informed by community input. The pandemic has caused disruptions to several grant programs, but AST is working to remedy this. Astronomy and Astrophysics Research Grants are currently being awarded with a success rate of roughly 1 in 5, which is standard. Neff reminded attendees of the deadlines for different AST grants as well as grants in other divisions that astronomers could be eligible for. These grants include opportunities in data science and computer engineering. Neff wrapped up by introducing the new guide to NSF proposals and research.gov as a resource.
Zauderer wrapped up the town hall by discussing the NSF’s efforts on protecting spectrum use for astronomy. She referred attendees to the plenary by Sandra Cruz-Pol and James Lowenthal earlier today for a deep dive into the issue. The NSF would like to expand its efforts in radio spectrum management and extend these efforts to optical wavelengths. Zauderer mentioned that private companies like SpaceX have been amenable to mitigating harm to astronomy. To that end, she highlighted the Satellite Constellations 1 Workshop, a joint effort between the AAS and NOIRLab that will bring together “astronomers, satellite operators, dark-sky advocates, policy-makers,” and others to discuss the impact of satellite constellations. She also highlighted the NSF’s Spectrum Innovation Initiative, which would offer funding to parties interested in this issue.
Space Telescope Science Institute (STScI) Town Hall (by Amber Hornsby)
Opening the Space Telescope Institute (STScI) town hall today was the director of STScI, Dr. Kenneth Sembach, who started with a general update of operations. The key take-away message from the director is, “we are here to support and help you advance scientific discovery.” Naturally some activities have been impacted by COVID-19, but things are slowly starting up again with seminars, proposal evaluations, and more being re-imagined for online platforms.
Next on the agenda for Sembach was discussion of a very exciting project — the Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES). With a grand total of 1,000 orbits, this is the largest single Hubble Space Telescope (HST) program ever executed, and it has two primary objectives: (i) 500 orbits to extend the spectroscopic library of O and B stars of low metallicity and (ii) 500 orbits to create a spectroscopic library and time monitoring of T-Tauri stars (younger than 10 Myrs). The first data release of the Small and Large Magellanic Clouds will be in September 2020.
Illustration of NASA’s WFIRST telescope, now the Nancy Grace Roman Space Telescope. [NASA]
The final, and possibly most exciting, part of Sembach’s talk was presenting the Wide Field Infrared Survey Telescope (WFIRST) as the Nancy Grace Roman Space Telescope. “NASA could not have chosen a better person,” said Sembach, because “she loved the universe.” This is where the STScI and NASA asks for help from the community. “We want and need to know how you will use the Nancy Grace Roman Space Telescope.” Please participate in an open community survey by June 15.
Moving on to a big problem in modern astronomy — Dr. Joshua Peek discussed large data sets and improving their accessibility. As new instruments come online and take an unprecedented amount of data, it becomes more and more challenging to ensure everyone can access the archived data and that they can do exciting science with it. STScI has already started tackling this problem with a NASA-funded project, the Milkulski Archive for Space Telescopes (MAST), which collates data from the HST, the Transiting Exoplanet Survey Satellite (TESS), and Kepler.
Data are getting BIG, now over a petabyte. Number of institutions per paper is also growing, the median is now five! #AAS236pic.twitter.com/jK0K7XtaFj
So far, astronomers are already making great use of MAST to write an impressive number of papers, which has highlighted another trend in astronomy: the number of institutions represented on a paper. The median number of institutions for every paper published using MAST data is now 5. This represents another problem facing many groups: the problem of each member being able to access data sets and work on them simultaneously. Here, Peek introduces the Time series Integrated Knowledge Engine, otherwise known as T.I.K.E.
T.I.K.E is a public, cloud-based Jupyter lab environment which contains pre-installed software for interpreting time series data, the kind associated with the study of exoplanets. Not only are your usual python packages like Numpy and Scipy built in alongside key packages for astronomy, like Astropy, but T.I.K.E also includes specialised packages created to work with time series data such as Exoplanet. All of this is useful, but what makes T.I.K.E next-level is access to TESS and Kepler data through the platform, the built-in notebooks and shared repositories for collaborations. Through T.I.K.E, the learning curve to participate in astronomy will be reduced, which will “accelerate science” and enable scientists to “find more stuff”, more quickly. T.I.K.E will be available sometime this summer.
Next up, Dr. Karoline Gilbert presents ‘Hundreds of Hubbles in the 2020s: realising the scientific potential of the Roman Space Telescope Archive’. Having recently passed the “formulation” phase of the mission, we’re now moving towards “implementation,” meaning the design has been finalised, thus hardware is now in development, and flight detectors are being built and delivered.
With a Hubble-sized primary mirror of 2.4 meters, we can already anticipate beautiful Hubble-quality images from the Roman Space Telescope when it is launched within the decade, but what is particularly revolutionary is its field of view. Having a larger telescopic view allows large areas of sky to be mapped faster. For example, the Roman telescope can measure the complete satellite and cluster populations of a galaxy, capturing the extent of the dark matter halo, with Hubble-like sensitivity and resolution in one pointing. For nearby galaxy surveys, like the Panchromatic Hubble Andromeda Treasury (PHAT), the Roman Telescope can map the same region almost 1,500 times faster.
Furthermore, data from the Roman Space Telescope will be publicly available with no proprietary period, via a T.I.K.E-like environment. This is an exciting step forward towards a more open and accessible field of astronomy, which will enable an impressive amount of science to be done by astronomers all over the globe. Currently, the team predicts proposal opportunities will be available at the beginning of 2021 and invites astronomers to participate in a virtual conference focused on the future of galaxy formation and evolution studies in October.
To close out the town hall, Dr. Louis Strolger reports on the recent HST proposal cycle 28 and the changes implemented in the review process. To address the COVID-19 impact, the proposal deadline was extended and the review was completed entirely via virtual platforms. Another recent change that also occurred for the last two cycles was a dual-anonymous review hiding the identities of proposers throughout the scientific ranking phase. This process is having an important impact on the gender diversity of proposers.
Over the last three cycles, the gap in proposal acceptance rate between male and female PIs has decreased from an average of 5% to 1%, with a predicted increase of female-led proposals of 0.5% per year. Furthermore, the number of PIs being awarded programs for the first time is also on the up, suggesting the dual-anonymous process is allowing the next-generation of scientists to get telescope time. Due to its success, the dual-anonymous review process will continue to be implemented and will also be used for James Webb Space Telescope (JWST) proposals, which are expected to be due in late fall.
Press Conference: Planets, Exoplanets & Brown Dwarfs (by Haley Wahl)
The second press conference of the day focused on planet-like objects!
Phobos as seen by Mars Express. [G. Neukum (FU Berlin) et al., Mars Express, DLR, ESA; Peter Masek]
First up was Matija Cuk from the SETI Institute speaking about Mars’s moons. The planet Mars has two moons: Phobos and Deimos, both of which were previously thought to be captured asteroids. However, by looking at the orbital inclination of Deimos, this team found evidence of a past Martian ring that created what is now Phobos — and that ring was formed from a “proto-Phobos” which was 20x the current mass of Phobos. This, his team believes, is only the latest case in a cycle of a moon becoming a ring and then the ring becoming a smaller moon. Press release
Next up was Fritz Benedict from the University of Texas, Austin to talk about calculating the mass of the recently identified, nearby planet Proxima Centauri c. By revisiting 25-year-old Hubble data, combined with some newer results from 2020, his team finds that the mass of Proxima Centauri c is either that of 18 Earths or 7 Earths, depending on which measurements are included in the calculations. Though there is still work to do, this finding shows that you can indeed find new results from old data. Press release
The third speaker was amateur astronomer Paul Benni from the Acton Sky Portal. He discussed the first discoveries of the Galactic Plane Exoplanet Survey (GPX). The first of these new discoveries is KPS-1b: the first transiting exoplanet (a hot Jupiter) discovered using an amateur astronomer’s wide-field CCD data. Another major discovery was GPX-1b, a transiting brown dwarf orbiting an F star. This was not detected by TESS algorithms because the host star was <1 arcmin away from a really bright star, so it diluted away the transit signal. The final discovery: a pre-cataclysmic binary with unusual chromaticity of the eclipsed white dwarf! Read more about Paul’s work in his paper.
Illustration of a brown dwarf surrounded by a disk. [NASA/William Pendrill]
The final speaker of the press conference was Maria Schutte (@maria_schutte), a PhD student at the University of Oklahoma. She discussed the citizen science project Disk Detective, which allows people at home to find new planet-like systems. This project led to the discovery of W1200-7845, an especially young (~3.7 Myr), nearby (332 light-years) brown dwarf disk! W1200-7845 provides us with a unique opportunity to study a potentially planet-forming disk around a nearby brown dwarf. To learn more, follow @diskdetective on Twitter. Press release
Plenary Lecture: The Atacama Cosmology Telescope and the Simons Observatory: The Millimeter-Wave Sky from Chile (by Amber Hornsby)
For the final plenary of day 2 at AAS 236, Prof. Jo Dunkley (Princeton University) presents the millimeter sky as viewed by the Atacama Cosmology Telescope (ACT) in Chile, and plans for a next-generation cosmology telescope, the Simons Observatory (SO). Throughout the plenary, there is a focus on the cosmic microwave background (CMB) and what it tells us about the universe; however, we also learn about bonus discoveries that can be made with detailed surveys of the millimeter sky.
The CMB is often referred to as the “afterglow of creation” because we’re looking at the oldest photons in the universe. Initially, the universe was a hot, opaque soup of interacting photons and baryons. After 380,000 years, the universe had expanded and cooled enough for photons to escape, and this is the remnant light we can observe today. When observed for the first time in 1964, it appeared to act like a perfect, uniform blackbody with a peak temperature of 2.74 K and peak wavelength of around 2 mm. But, thanks to improved measurements, we now know there are actually tiny temperature fluctuations in the CMB.
The best known, most recent image of the CMB is from the Planck Satellite. We see the seeds of our large scale structure from fluctuations in the primordial plasma. Isn't out baby universe cute? #AAS236pic.twitter.com/omKzsfSvZk
The temperature map, created using data from the Planck space telescope, is a nice snapshot of the physics of the universe at a redshift of z = 1,100. The intensity of the CMB mainly tells us about the density of the photon-baryon plasma, where hot spots (shown in red) represent denser regions. Dunkley explains how, if the map is decomposed in terms of angular scale, we can plot the amount of “bumpiness”, the so-called power spectrum of the sky. Given this, we can theoretically predict different model universes, containing different initial ingredients and conditions until our predictions fit the observed data. The best-fit model to Planck data is given by a Lambda-Cold-Dark-Matter (LCDM) cosmological model requiring three ingredients and two initial conditions.
The CMB is a backlight to every other signal we see, and so it sensitive to universe effects, including lensing, the tSZ, and the kSZ. #AAS236pic.twitter.com/PxIfzN7fdw
As CMB photons travel through the universe, they encounter galaxies, hot electrons and more, which alter the photons in some way. For example, CMB photons are very sensitive to massive objects, which results in the lensing of the CMB. It is further distorted by the thermal and kinetic Sunyaev-Zel’dovich (SZ) effect. The thermal SZ effect is where hot electrons scatter the CMB, causing a shift in its observed spectrum, whilst the impact caused by the momentum of high-energy electrons is characterised by the kinetic SZ effect. It is important to characterise these effects to get an accurate picture of the CMB.
However, something that CMB enthusiasts can forget is the “wealth of information” contained within surveys of the millimeter sky beyond the CMB. Dunkley points to observations of polarised dust taken by Planck. Although dust contaminates our CMB signal, we can infer the orientation of the magnetic fields in our galaxy through the alignment of dust grains by simply rotating the polarisation signal by 90 degrees. This is because dust grains align themselves perpendicular to the magnetic field. But this is only the start. Surveying the millimeter sky addresses other key astrophysics questions, such as (i) how long did reionization take? (ii) where is Planet 9? (iii) is the accelerated expansion of the universe just Lambda?
Dunkley now introduces ACT, and how it builds on Planck’s legacy. ACT has been operating since 2007 and its third-generation instrument has around 5,000 detectors. There are a few differences between ACT and Planck, such as ACT only mapping 40% of the sky and being ground-based. However, ACT data have 3 times less noise than Planck data and are much better resolved. In recent ACT maps, this has uncovered radio galaxies (blazars) and galaxy clusters through the SZ effect. Moreover, ACT has observed the largest-ever SZ galaxy cluster sample containing over 4,000 clusters!
ACT also adds to resolution in the polarization signal — here, the E-field polarization is shown. White is less and black is more polarized than average. Though it looks noisy, we really can see fluctuations in velocity from the early universe. #AAS236pic.twitter.com/ky6qy5LJgH
Additionally, ACT has captured unprecedented views of the polarised sky at 2 mm, the signal size of which is known as the E-mode component of polarisation. Here, white represents higher polarisation on the grey-scale image. We can also create a power spectrum based on ACT data which, combined with data from the ground-based telescopes POLARBEAR and the South Pole Telescope (SPT), can provide an independent calculation of the contentious Hubble constant. A paper on this new result is currently in preparation.
Sadly, Dunkley reveals, we have hit an upper limit on the number of detectors we can fit in the telescope. This is important because without more detectors, we cannot make further reductions in the noise in our observations. We thus need to consider a new telescope — Simons Observatory. Already under construction, the 6-meter-primary telescope will live alongside ACT in Chile and will house over 30,000 transition-edge sensor detectors.
This impressive telescope will have a huge impact on the millimeter community, providing new opportunities to participate in transient science through synergy with multiple surveys. SO plans to track thousands of variable active galactic nuclei on a daily/weekly/monthly basis at 1–10 mm wavelengths. With an observing timeline of 2023–28, SO will overlap with the Vera Rubin Observatory, the Dark Energy Spectroscopic Instrument (DESI), and Euclid, enabling observations to be completed simultaneously at different wavelengths. In addition to the substantial improvements in CMB observations, including the potential for a glimpse of the elusive B-mode component of the polarised CMB, SO will also observe 30,000 high-redshift, dusty galaxies and 20,000 clusters.
In her closing remarks, Dunkley reminds us that there is “so much to learn from wide-field surveys of the millimeter sky.” We can learn about our galaxy, transient sources, AGNs, and my favourite, the CMB, which gives us a “unique view of the early universe.” ACT scientists are looking forward to sharing new data and software with the astronomical community — so keep an eye out for upcoming press releases.
Editor’s Note: This week we’re at the 236th AAS Meeting, being conducted virtually for the first time! Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume the week of June 8th.
Welcome Address (by Sanjana Curtis)
AAS President Megan Donahue (Michigan State University) kicked off the 236th meeting of the American Astronomical Society — the first AAS meeting that is entirely virtual. Before opening the meeting, she acknowledged the fact that many members of the astronomy community are not present due to a variety of factors, including a pandemic, the choices of others, and an uninterrogated system that grants privileges to a select few. This was a sobering reminder that science is, above all, a human endeavor.
As a virtual meeting, this AAS has a low carbon footprint that is certainly good news for the environment. At the same time, the meeting attendance is almost double the usual attendance at in-person meetings, including twice as many students! There are scientists from 34 countries and 49 of the 50 US states (with the exception of Alaska) in attendance. The schedule is packed, the science is exciting, and we’re looking forward to 3 days of hearing about the latest research and the newest results in astronomy!
AAS President Megan Donahue’s welcome acknowledgements.
Fred Kavli Plenary Lecture: Searching for Habitable Worlds: Challenges, Opportunities & Adventures (by Sanjana Curtis)
Lisa Kaltenegger (Carl Sagan Institute) delivered the Fred Kavli Plenary Lecture and spoke about the challenges, opportunities, and adventures to be found in our search for habitable worlds. Starting from being able to observe just a handful of exoplanets, we have now reached a point where we can start doing statistics with them. We have found thousands of new worlds that show great diversity in their properties, and exploring this diversity through theoretical modeling can help us understand the physics of both the planets and their host stars. A wonderful review on this topic can be found here.
Kaltenegger presents a radius vs. mass plot of measured exoplanets. Click to enlarge.
Dr. Kaltenegger also addressed whether we can distinguish the population of rocky planets from the population of gas planets based on the mass and radius of the exoplanet. If we know both the mass and the radius of an exoplanet, we can derive its mean density and composition, and compare it to planets in our solar system. However, for most exoplanets, either the mass or the radius is known depending on the detection method. In general, the line dividing gas planets from rocky planets sits at around 2 Earth radii—all exoplanets below this limit are rocky planets.
Kaltenegger’s group has created a catalog of exoplanet spectral fingerprints.
The spectra of exoplanets are key to understanding their properties and Dr. Kaltenegger’s research group is creating a database of spectral fingerprints to compare against future observations by telescopes like ELT or JWST. These data are freely available here. She stressed that we do not just have the current Earth as a template for habitable planets, but also the Earth through time.
She ended her talk with some intriguing and adventurous ideas: the possibility that organisms on planets around active M stars may develop biofluorescence to protect themselves from harsh ultraviolet light, and the existence of habitable worlds around red giants and white dwarfs!
The second press conference of the day involved new studies on some galactic oddities! Four scientists took turns sharing what they’ve discovered lurking in our cosmic neighborhood.
Satellite galaxies of NGC2998 have a “lopsided” distribution. This image shows how there seem to be more satellite galaxies (circled in yellow) on one side of the host galaxy (circled in blue) than the other.
First, Tereasa Brainerd (Boston University) shared her team’s findings that involved the distribution of satellite galaxies around a host galaxy. Scientists believe that the dark matter halos that surround galaxies (as predicted by the cold dark matter theory) are spherical, flattened elliptical halos. By looking at the systems with 5+ satellites around the host galaxy, they found “lopsided” distributions, meaning there were more pairs of galaxies on one side of the galaxy than the other. Could this have implications for cold dark matter? It’s possible!
Next up was Lior Shamir (Kansas State University) who continued the theme of asymmetries. He presented observations that showed that the distribution of apparent spin directions of galaxies isn’t always symmetric, that it changes depending on the direction of observation. He also showed that the direction of spin is linked to its brightness and that asymmetry varies with redshift. Press release
The extent of the hot circumgalactic medium around the galaxy studied by Das’s team.
The third speaker was Sanskriti Das (Ohio State University), who talked about evidence for a massive hot circumgalactic medium around a luminous star-forming galaxy. She and her team showed, using X-ray data, that this material, which is extended over a large volume and has a large mass (comparable to the mass of all the stars in that galaxy!), could be the solution to the “missing baryons” problem in galactic halos. Press release
The last speaker of the press conference was Ripon Saha (University of Missouri, Kansas City), who presented the discovery of a massive proto-supercluster 10 billion light-years away. Using a pipeline made using dust-obscured galaxies (DOGs), he and his team identified the proto-supercluster of galaxies surrounded by nascent ones. This is the first time any observed cluster has been found embedded in its birth environment, which could give astronomers a unique opportunity to study such a cluster.
Plenary Lecture: The Inclusion Revolution (by Luna Zagorac)
The midday plenary entitled “The Inclusion Revolution” was delivered by Dr. Dara Norman, the Deputy Director of the Community Science and Data Center at NSF’s NOIRLab in Tucson, AZ. Dr. Norman began her plenary by describing the term “culture”: the customs, institutions, and achievements of a group of people. As scientists and astronomers, we have our own culture — including our language, our traditions, our norms, our values, and even our art — and parts of this culture must be changed to support diversity and inclusion in astronomy. Indeed, culture is not a static object: an example of cultural change comes from the very first decadal survey, which addressed the demographics of the workforce and the lack of availability of public telescopes. This led to the funding of the national observatories, without which the state of astronomy today would look completely different, underscoring the potential impact of the 2020 and future decadal surveys.
The AAS decadal survey has always been a tool for assessing the demographics of astronomers conducting research, and for changing culture. Indeed, the first one ever published fueled the founding of national observatories due to lack of access to telescopes nationwide!
A point that Dr. Norman emphasized throughout her plenary is a quote from Paula Stone Williams’s TED talk — “I didn’t know what I didn’t know.” The first step towards inclusion is thinking about not just who is represented on policy-making committees, but what kind of expertise is represented. It’s not enough to have a lot of different voices if there isn’t a critical mass of expertise in the room. Additionally, we need to empower each representative to act as a mouthpiece for their community, while gathering ideas and thoughts from the community. In this way, the issue of having too many people on committees can be avoided, and the workload redistributed amongst individuals.
The blue area represents the papers written on data from dedicated HST observing runs, while the orange represents papers from archival data. Note that the numbers equal out with time!
Next, Dr. Norman discussed her paper (Norman 2018), which explored how to use big data to reach insider status in the field — including being invited to join collaborations, give talks, review papers, and more. She found that, with time, the number of papers published on data from allocated Hubble time evened out with the number of papers written from archival data. Findings from Peek et al. (2019) broke that down by authorship, and the gap was significantly larger at small and underfunded institutions. This raised the question of whether archival data can be used as a vehicle to accessing the dedicated observation time that is critical for advancing in the field.
Figure from Peek et al. 2019. The blue line represents HST papers published using archival data, while the orange represents papers stemming from dedicated observing time. Note the discrepancy between large and small institutions!
Dr. Norman is looking for a 3-year postdoc (click to enlarge)! The posting is not out yet, but you can contact Dr. Norman via email for more details.
Going back to the general theme of “you don’t know what you don’t know,” the first step to bridging this gap is to directly ask colleagues at small and underserved institutions what they need. One of the needs Dr. Norman identified was the need for more policies and incentives for R1 institutions to work with smaller institutions, as is currently rarely the case. To this effect, Dr. Norman will be working on a toolkit for effective diversity and inclusion practices and their efficacy, particularly aimed at underserved institutions. She will be looking for a 3-year postdoc to aid in this effort, and can provide more information upon email request.
Dr. Norman ended her talk by underscoring that there is much more work to do on diversity and inclusion in astronomy, including through the decadal surveys, which have been a tool for demographics-driven cultural change from the very start. She closed by reminding us that we need change; that the revolution will not simply be tweeted; that black lives matter; and to vote.
NASA Town Hall (by Abby Waggoner)
The NASA Town Hall was led by Paul Hertz, Director of the Astrophysics Division in the Science Mission Directorate at NASA. The NASA Town Hall provided an overview of NASA operations, funding, and missions from the past year, along with goals and funding for the future. Below, each topic covered is summarized in bullets. All images are obtained from the slides provided during the town hall.
Where does NASA Astrophysics funding go? The numbers shown in this figure shows that the funding goes to supporting many scientists and projects!
Committed to Improving
Mission PI Development: NASA seeks to increase the diversity of mission principal investigators.
Fellowships and funding for graduate students and postdoctorates were awarded, including:
Nancy Grace Roman Technology Fellowship
Hubble Fellowship
NASA Earth and Space Science Fellowship (NESSF)
Future Investigators in NASA Earth and Space Science Technology (FINESST).
Peer reviews have become anonymous.
Mission Program Update
Impact of COVID-19: Flight operations have continued nominally with the exception of the Stratospheric Observatory for Infrared Astronomy (SOFIA has been grounded; see below).
Priority has been given to Mars 2020 and the James Webb Space Telescope (JWST).
Updates from missions currently in flight:
Hubble had its 30th birthday. You can find out what Hubble was imaging on your birthday here.
The Transiting Exoplanet Survey Satellite (TESS) has discovered 47 confirmed planets and 1,837 planet candidates. The four-planet system HD 108236 was highlighted, as the three outer planets are candidates for spectral analysis with JWST.
SOFIA has suspended flight operations since March 2020 due to COVID-19. There will be a community update on SOFIA on June 2 at 3pm (EDT) during AAS 236.
NASA has 10 missions planned for the future. These missions include a science goals ranging across the entire electromagnetic spectrum.
Updates from among NASA’s 10 missions currently in development:
JWST has undergone deployment testing, and will soon begin observatory-level environmental testing.
Roman Space Telescope (formerly Wide-Field IR Survey Telescope, or WFIRST) is fully funded and in production. Roman will aid in understanding the evolution of the universe to exoplanet direct imaging.
Two small explorers are planned:
ESCAPE will investigate UV stellar flares and their impact on the habitable zone.
COSI will observe MeV gamma-rays to trace the Milky Way’s supernova activity.
Two missions of opportunity are planned:
Dorado will watch for UV light emitted by merging neutron stars.
LEAP will be attached to the ISS and observe the polarization of gamma-ray bursts in jets.
NASA funding for the 2020 year and how the funding is being allocated.
Planning for the Future
NASA funding for the Astrophysics Division is at an all time high, with 58% of the funding dedicated to JWST and Roman.
NASA seeks to have humans sent to the moon by 2024 through the Artemis Project.
In the next decade, NASA has concepts for several medium and large missions in the 2020 Decadal Survey.
Press Conference: Cosmic Bangs & Whimpers (by Alex Pizzuto)
Deborah Schmidt (Swarthmore College) kicked off this afternoon’s press conference by summarizing her dissertation work, which focuses on the abundance of different atomic isotopes in planetary nebulae. While many of us may know of planetary nebulae, such as the butterfly nebula, for their strikingly beautiful silhouettes, these objects “also play a significant role in the recycling of matter in our universe,” according to Schmidt.
Planetary nebulae are the final stages of Sun-like stars. Towards the end of their lives, stars can eject material that flows away from the remnant core and enriches nearby interstellar regions, filling it with a wide array of elemental isotopes that were originally produced in nuclear reactions within the star. Until recently, it was thought that these isotopes shouldn’t linger very long, because the hot white dwarf remnant at the center of this nebula should produce a plethora of high-energy radiation, which has the potential to destroy the expelled molecules.
Schmidt presented recent radio observations that challenge these beliefs, and found that these regions, although expected to be cleared out of these elemental abundances, were instead “bursting with molecules.” This wealth of elemental isotopes was found in both the young and old nebulae that Schmidt studied, and this discovery has major implications for a breadth of topics. These include potentially remedying tensions relating to the prevalence of poly-atomic ions in the diffuse interstellar medium, as well as explaining the previously anomalous origins of dust grains that are present even in our own solar system. Additionally, these observations allowed Schmidt and collaborators to build a new model of the inner workings of planetary nebulae, and to show how potentially explosive origins can not only explain the prevalence of a variety of elemental isotopes, but can also explain the gorgeous shapes of planetary nebulae that we know and love.
Schmidt describes the plethora of elemental isotopes that originate in planetary nebulae and explains how these objects explain the anomalous abundances of elements in the diffuse interstellar medium.
Adelle Goodwin (Monash University) then went on to describe recent observations of extremely energetic outbursts visible across nearly the entire electromagnetic spectrum: accreting pulsars. Accreting pulsars consist of neutron stars, the dense remnants of dead stars, in close orbit with a “normal” star. Neutron stars are so dense that a mere handful of their material would have the same mass as about 5 Mount Everests, or 5 billion tons. If in orbit with a nearby star, these neutron stars can slowly consume their companions, filling up accretion disks until reaching a critical threshold, and then quickly gobbling up some of this material and expelling a fraction of it in a violent outburst.
Artist’s impression of an accreting pulsar. [NASA]
This outburst should be visible in a variety of electromagnetic wavelengths, including optical, UV, and X-ray, and the evolution of the radiation in these different wavebands reveals a wealth of information about the underlying processes that are occurring. Goodwin describes the first ever set of observations of this entire outburst period with simultaneous coverage in these various wavelengths. Specifically, her team targeted a pulsar located 11,000 light-years away, spinning 400 times per second, and they observed this pulsar with more than 7 telescopes. As Goodwin and her team investigated this object, they noticed that the X-ray emission began at a time much later than the optical emission, with a delay of about 12 days, longer than any model would have predicted. The team was able to reconcile this discrepancy by suggesting that the disk consists of a large fraction of helium, which takes longer to heat up and then ionize. Regardless of the delay of X-rays, these observations of an outburst thousands of times brighter than the Sun marks a new step in understanding the dynamics of these explosive transients. Press release
Next up was Justin Vandenbroucke (University of Wisconsin, Madison) on behalf of the Cherenkov Telescope Array (CTA), a team of scientists dedicated to investigating the universe at the highest energies. Some objects in our own galaxy are capable of producing particles of light with energies exceeding one tera-electronvolt (TeV), which is about one trillion times more energetic than the particles of light we detect with our own eyes. Studying this light, and the objects capable of producing it, teaches us about the most efficient and energetic accelerators in our universe.
In order to detect these particles, Vandenbroucke described a prototype ground-based gamma-ray telescope. When a gamma ray approaches the Earth, it can demolish an atom in the atmosphere. This collision produces a menagerie of particles travelling at nearly the speed of light, which in turn produce tiny flashes of blue light. The goal is to then reflect these tiny blips of blue light into a camera by building precise and gargantuan mirrors on the ground. In case that does not sound difficult enough, Vandenbroucke described how this telescope features a two-mirror design as well as state-of-the-art electronics. This symphony of advanced electronic and complicated optics should be able to come together to produce some of the most vivid and detailed pictures of the universe in its most energetic states.
To test out this new telescope, Vandenbroucke and his team pointed their telescope at the Crab nebula, the remnant of an exploded star from 1,000 years ago, which features a pulsar in the center powering very bright emission up to TeV energies. The team was able to significantly detect this object at these amazingly high energies. Vandenbroucke noted that this “detection establishes innovative telescope technology for gamma-ray astronomy.” Together with the other telescopes being constructed, the CTA consortium should revolutionize the way we see the universe and will play a pivotal role in both multi-wavelength and multi-messenger astronomy at the highest energies. Press release
Vandenbroucke shows the first detection of the Crab nebula with this revolutionary high-energy gamma-ray telescope, providing a picture of this object at energies trillions of times more energetic than we detect with our eyes.
Wrapping up today’s press conference was Fabio Pacucci (Black Hole Initiative & Center for Astrophysics), discussing how black holes grow. We know that black holes come in a variety of masses, ranging from those just a few times more massive than the Sun all the way to millions of times more massive than this. What we don’t know is how these black holes get to be so large.
Fabio Pacucci’s conclusions for how black holes of different sizes grow at different times in the universe. Click to enlarge and read text. [Illustrations: M. Weiss]
Fundamentally, there are two ways a black hole can acquire more mass: either they slowly accrete matter from their nearby environments over time, or they merge with other black holes, and in a short period of time create one larger black hole nearly as massive as the sum of the two individuals. Pacucci discussed a set of simulations aimed at deciphering which black holes are accretion-dominated and which are merger-dominated.
Pacucci found that for nearby black holes, lighter black holes are more likely to gain mass via accretion and heavy black holes via mergers. What’s bizarre is that if you peer out to black holes farther away from us, then the exact opposite is true, namely distant, light black holes are likely to acquire mass from merging and distant, heavy black holes are likely powered by accretion. This is important because the growth mechanism has implications for the spin of these systems, as black holes that grow from accretion are likely to spin much faster than those that grow from mergers. This has direct observational consequences, as spinning black holes should be more efficient at emitting radiation and thus may be easier to observe with electromagnetic observatories, whereas black holes that are growing from mergers are likely best detected with gravitational wave detectors. Pacucci summarized this nicely, noting that “this [study]will inform decisions regarding observational strategies with future space telescopes, as well as lay the basis for models that describe other aspects of the evolution of the universe.” Press release
Plenary Lecture: Journey to the Center of the Galaxy: Following the Gas to Understand the Past and Future Activity of Galaxy Nuclei (by Abby Waggoner)
Our final plenary lecture of the day was given by Elisabeth Mills from the University of Kansas. Dr. Mills discussed the “Journey to the Center of the Galaxy: Following the Gas to Understand the Past and Future Activity of Galaxy Nuclei” and brought us from our solar system to the center of the galaxy, 26,000 light-years away. In this journey, we explored how different wavelengths of light can be used to understand the past (and future) of a black hole in the center of a galaxy.
The center of our galaxy, zoomed further and further in at different wavelengths. Note that we use different types of light for each image, to see further and further into the center.
When we look towards the Milky Way’s black hole, Sgr A*, clouds of dust between us and the black hole absorb all optical light, so we have to use other wavelengths of light — such as infrared, radio, and millimeter — to observe the galactic center. Each type of light tells us something different about what’s happening in the center of the galaxy. Radio wavelengths show us the light of past generations of stars, or those that have died and experienced a supernova. Infrared wavelengths show us the “stars of today,” by letting us see the dust warmed by stellar radiation. Millimeter wavelengths show us the “stars that will be” by revealing the location of cold gas and dust that will eventually collapse to form a star. Together, these wavelengths will help us in understanding the past, present, and future activity of the black hole in the center of our galaxy.
The gas and dust in the center of our galaxy is hotter, denser, and more turbulent than the gas and dust in the interstellar medium. This raises the question: Why is the dust at the center of the galaxy so different?
As H2 molecules collide with HC3N, HC3N rotates and emits energy. More dense regions result in more collisions, and the emission of light with a lower wavelength.
To answer this, astronomers consider the light emitted by rotating molecules, such as HC3N. When molecules collide with other molecules (such as H2), the kinetic energy of the collision causes the molecule to spin, or become “rotationally excited.” When there are a lot of collisions, such as in a high density region, the molecule spins at a higher frequency/energy. This allows us to probe the density of dust and gas near the center of the galaxy by observing these different rotation energies.
When astronomers look towards the center of the galaxy, we find that the gas and dust density drastically drops around 350 light-years from Sgr A*, where more than 99.9% of all the dust mass in the center of the galaxy is beyond 350 light-years from the black hole. This is evidence of strong intense shocks released by Sgr A*. However, our black hole is currently not active enough to explain this mass drop. This indicates that our black hole wasn’t always “boring,” and used to be much more active.
Based on observations of these four galaxies, we can see a variety of black hole activity and star formation. This allows us to get a more clear picture of the evolution of galactic centers.
Thanks to telescopes such as ALMA and Hubble, this technique can also be used to explore black holes in other galaxies, thus giving us a broader picture and understanding of the evolution of galaxies.
AAS Nova Editor Susanna Kohler and AAS Media Fellow Tarini Konchady will join Astrobiters Sanjana Curtis, Abby Waggoner, Haley Wahl, Luna Zagorac, Alex Pizzuto, and Amber Hornsby to live-blog the meeting for all those who aren’t attending or can’t make all the sessions they’d like. We plan to cover all of the plenaries, press conferences, and town halls, as well as a few additional sessions, so follow along here on aasnova.org or on astrobites.org!
We’re sad not to get to talk to you in person, but we’re pretty psyched about the virtual setup for this meeting. We look forward to seeing you in sessions and visiting your posters throughout the next three days.
Where can you find us? Astrobites Media Intern Sanjana Curtis will be presenting a poster about Astrobites in the iposter gallery on Wednesday, 3 June, 5:30–6:30pm ET. Drop by to check it out and say hello — it’s poster 339.04: Astrobites: Accessible Summaries of the Latest Astrophysics Research.
In addition, if you’re registered for the meeting, we’d love for you to stop by and visit us this week! You can find us at the AAS Resource Center in the Exhibit Hall — we’ll be staffing the booth daily during the breaks from 9am-10am ET, 1:40–2:40 ET, and 5:30–6:30 ET, and we’re always happy to hear from you.
Lastly, if you’re interested in reading up on some of the keynote speakers before their talks at the meeting, be sure to check out the interviews conducted by Astrobites authors, linked below! This is a great opportunity to discover more about these prominent astrophysicists and learn about the path they took to where they are today.
Will you be joining us online for the 236th American Astronomical Society meeting — our first-ever virtual meeting? AAS Publishing looks forward to seeing you there! You can come find us at the AAS Publishing booth in the virtual exhibit hall, and you can check out AAS-Publishing-related endeavors in a number of events throughout the week. Below are just a few.
AAS Publishing Exclusive: A Discussion with arXiv Executive Director Dr. Eleonora Presani
Tuesday, 2 June, 9:00 am–10:00 am EDT, Maria Mitchell Room.
iPoster Plus Presentation: Making Informative Interactive Figures for Time Series Data Sets, by Dr. Greg Schwarz
IOP Publishing Webinar: AAS Article Production and the Chandrasekhar Style Guide
Wednesday, 3 June, 11:00–11:30 am EDT, IOP Publishing booth in the exhibit hall. View the abstract here.
Chat Schedule at the AAS Publishing Booth
Want to chat with someone in particular at AAS Publishing? Here’s the schedule of when we’ll be at the AAS Publishing booth in the virtual exhibit hall.
Monday, 1 June
1:40–2:50 pm EDT
Brian Jackson, Planetary Science Journal Scientific Editor
Greg Schwarz, AAS Data Editor
Gus Muench, AAS Data Editor
2:50–4:20 pm EDT
Judy Pipher, AAS Lead Editor of the Interstellar Matter and the Local Universe Corridor
5:30–6:30 pm EDT
Greg Schwarz, AAS Data Editor
Tuesday, 2 June
9:00–10:00 am EDT
Daniel Savin, AAS Scientific Editor in Laboratory Astrophysics
10:00 am EDT onward
Eleonora Presani, arXiv Executive Director
1:40–2:50 pm EDT
Greg Schwarz, AAS Data Editor
Gus Muench, AAS Data Editor
2:50–4:20 pm EDT
Judy Pipher, AAS Lead Editor of the Interstellar Matter and the Local Universe Corridor
5:30–6:30 pm EDT
Greg Schwarz, AAS Data Editor
Wednesday, 3 June
9:00–10:00 am EDT
Daniel Savin, AAS Scientific Editor in Laboratory Astrophysics
11:00 am –12:30 pm EDT
Michael Endl, AAS Lead Editor of the Solar System, Exoplanets, and Astrobiology corridor
Daniel Savin, AAS Scientific Editor in Laboratory Astrophysics
Gus Muench, AAS Data Editor
1:40–2:50 pm EDT
Judy Pipher, AAS Lead Editor of the Interstellar Matter and the Local Universe Corridor
Available most times, all three days in the AAS Publishing booth:
Ethan Vishniac, AAS Editor in Chief
Frank Timmes, AAS Lead Editor of the High-Energy Phenomena and Fundamental Physics corridor
Janice Sexton, AAS Editorial Operations Manager
Julie Steffen, AAS Director of Publishing
You can find AAS Nova Editor Susanna Kohler and the Astrobites team at the AAS Resource Center booth.
Publishing Your AAS 236 Presentation in RNAAS
If you’re presenting research at AAS 236, consider publishing a brief Research Note about it in Research Notes of the AAS! We’ll be putting out a focus issue of RNAAS specifically for AAS 236 content after the meeting. For more information, see the announcement here.
In a small organization like the American Astronomical Society, everyone involved wears multiple hats. Chris Lintott — AAS Journals Lead Editor and Editor of Research Notes of the AAS — takes this paradigm to the extreme, adding his multiple roles at the AAS to an already impressively varied career.
Taking the Lead
“It turns out that one should be careful about expressing opinions,” Chris Lintott jokes as he explains how he became an AAS editor. In 2016, he challenged the AAS Journals’ 50-year-old policy to reject manuscripts describing software. AAS publishing listened — and then offered him the role of Lead Editor for the newly created Laboratory Astrophysics, Instrumentation, Software, and Data journal corridor.
AAS journals welcome the submission of articles describing astronomical software. [astropy]
One might think that the University of Oxford professor — who is the principal investigator of the Zooniverse project and is also known for his role as co-presenter of the BBC’s long-running astronomy program The Sky at Night — already had enough on his plate. But Chris accepted the Lead Editor position, and within days the AAS Journals’ new software policy was born: AAS Journals now “welcome articles which describe the design and function of software of relevance to research in astronomy and astrophysics”.
Since the change, Chris has been glad to see many software-related articles published by major collaborations; now he hopes to start seeing articles from people who write code for their own or their group’s use. “Think about spending a rainy Friday afternoon writing a three-page paper describing the software that [you’ve] worked hard on,” Chris suggests; in the modern era, this should be documented and citable in the same way that the science that’s produced with the software is!
Radio interferometric arrays like the MWA generate vast amounts of data. [Dr. John Goldsmith/Celestial Visions]
Chris’s corridor includes not only software, but also the extremely active community of laboratory astrophysics. It additionally covers instrumentation and all things data-related — a field that’s grown rapidly as large surveys arise and scientists need to develop new tools and techniques for dealing with them. “I like to think I get all the interesting papers,” Chris quips.
RNAAS: A New Type of Publication
As if this didn’t keep him busy enough, in October 2017 Chris took the lead on an idea that had been proposed as part of discussions about the future of AAS publishing: the development of an AAS journal where scientists could rapidly publish non-refereed, short results. Chris is the editor of the resulting Research Notes of the AAS, which provides a landing place for negative results, brief student projects, abandoned data, and more.
Research Notes of the AAS is a unique publication in the AAS journals family.
Since RNAAS’s launch, the journal has been embraced by the community. RNAAS has published nearly 500 articles in its 2.5 years, and almost half of these have been cited — a remarkably high fraction, given the informal nature of the journal.
“The thing that surprised me is the diversity of things that we’ve had [submitted],” Chris explains. “We’ve had the last observations with a particular telescope recorded for posterity. We’ve had how-to guides for complex statistical themes. We’ve had topical arguments about things like ‘Oumuamua, which helpfully shot through the solar system just as we were starting.”
Chris welcomes the diversity of RNAAS articles as well as those submitted to his AAS journals corridor. Wearing his two editor hats, he starts each day by checking on recent submissions. “To have a cup of coffee in the morning and not know what I’m going to read about is really exciting.”
Carving a Blurred Niche
What’s Chris doing when he’s not reviewing journal articles for the AAS? Though he initially studied the chemistry of star formation, his research now focuses on galaxy formation: in particular, what a large population of citizen scientists can help us to learn about galaxies and their formation. Chris runs Galaxy Zoo — which he describes as “a side project that went bonkers” — and the broad range of Zooniverse citizen-science projects that have grown out of it.
AAS Editor Chris Lintott at Jodrell Bank Observatory, UK. [Mike Peel]
In between research, editing, advising students, and teaching, he fits in travel and filming for the BBC’s The Sky at Night, conference visits, and giving frequent public talks. When asked about his somewhat unusual position at the interface between the worlds of scientific research, publishing, and public engagement, he argues that it’s not uncommon for scientists to wear multiple hats. “The more we blur the boundaries here, the better.”
Keep an eye out for Chris — wearing any one of his many hats — at upcoming AAS meetings. And send him your articles so he can read them over his morning cup of coffee!
Editor’s Note: This week we’re at the 235th AAS Meeting in Honolulu, HI. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume the week of January 20th.
Plenary Lecture: Diet of the Stars: Mass Accretion and Mass Loss (by Ellis Avallone)
“A picture is worth a thousand words, but a spectrum is worth a thousand pictures,” says Dr. Andrea Dupree (Center for Astrophysics | Harvard & Smithsonian). The first plenary of the day was on stellar spectroscopy, Dupree’s specialty, and the power it gives us in understanding stellar processes.
The talk focused on two main topics in stellar astrophysics: mass accretion and mass loss. There are many outstanding questions related to these processes, like their effects on the star, the star’s environment, and the planets around the star. However, answers to these questions remain conjectures until we can look at a star’s spectrum.
An ALMA view of TW Hya, a young star surrounded by a protoplanetary disk. [S. Andrews (Harvard-Smithsonian CfA)/B. Saxton (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO)]
Dupree then dove into discussing accretion. After a molecular cloud collapses to form a stellar core, an accretion disk forms around the young star. This accretion disk is threaded with the star’s magnetic field and material from the accretion disk is funneled along the magnetic field lines onto the surface of the star. Although this process sounds simple, showing that this theory is correct requires measurements of accretion in action in young stars. Dupree then discussed a case where we’ve directly measured accretion in the young star TW Hya. This star is unique in that the accretion disk is facing us (i.e. we’re observing the pole of the star). Because of this, astronomers have been able to make magnetic field maps of the pole and determine that the radial magnetic field varies with time.
To understand the accretion process in this system, Dupree then launched a campaign to observe TW Hya, a young star, in multiple wavelengths. Using spectra obtained by the Chandra X-Ray Observatory, Dupree was able to obtain full plasma diagnostics for the young star’s atmosphere and follow accretion onto TW Hya through time. “Veiling” was also observed — a process by which accretion onto the surface of the star produces emission that “fills in” absorption lines. This phenomenon has also been observed on the most well-studied star in the universe, the Sun. After a solar flare, material falls back to the solar surface, which produces the enhanced emission that causes veiling. Therefore, the Sun can act as a proxy when trying to understand accretion on young stars.
Illustration of the Parker Solar Probe spacecraft approaching the Sun. [NASA/Johns Hopkins APL/Steve Gribben]
Dupree then switched gears to discuss mass loss in stars, a complex process that affects everything from stellar evolution to the chemical enrichment of the interstellar medium to exoplanet environments. For this section of the talk, Dupree began with the Sun, whose solar wind carries material away from the Sun in a stream. Comet tails first indicated that there was an outflow of material coming from the Sun. This stream has now been well-observed via in-situ probes like the recently launched Parker Solar Probe and eclipse observations, allowing us to apply our knowledge of the solar wind to other stellar systems. Focusing again on TW Hya, Dupree discussed what had been discovered about its stellar winds (with spectra!). The wind of TW Hya is highly structured and was found to be variable by utilizing a near-infrared transition of helium. Dupree also mentioned that this same helium line can also be used to observe winds from gaseous exoplanets via transmission spectroscopy.
Dupree concluded her talk with a discussion of Betelgeuse, which has been a hot topic recently. It’s been fading and is the faintest it’s been in nearly 50 years. Does this mean it’s about to go supernova? We’ll just have to wait and see. This, and other unanswered stellar questions may soon be answered by a spectroscopist near you.
Special Session on Mauna Kea (by Mia de los Reyes and Ellis Avallone)
This special session focused on Hawaiian perspectives on Maunakea and the Thirty Meter Telescope. The panel consisted of four kānaka maoli (indigenous Hawaiians) and was moderated by Noelani Kalipi (Kohala Institute, Executive Director).
The panel began with a presentation from two kia’i, or protectors of the mauna. The first speaker, Pua Case, one of the leaders of the Ku Kia’i Mauna movement, sought to set the tone of the session. Protectors of Maunakea practice kapu aloha, a philosophy of nonviolence that has been heavily present in the movement to protect Maunakea. Case went on to say that “the focus of [the session]was not to debate.” Rather, the focus of this special session was to listen and learn from each other, and its purpose was to transport astronomers to the mauna and invite them to visit and learn.
Case then played a video that urged the audience to think about what is sacred and to work to understand the relationship between the people and the sky. The short film concluded directly: “We [kia’i] speak for the mountain and the mountain says no.”
Case then discussed ceremony that takes place at the Mauna, demonstrating the chant done on the Mauna three times a day. Case also outlined the importance of bringing offerings — something meaningful brought for the land or elders.
Mauna Kea, as viewed from Mauna Loa Observatory. [Nula666]
The next kia’i speaker was Lanakila Mangauil, who started his presentation by discussing his upbringing. Mangauil was part of the generation that was not kept from learning ancestral practices and wisdom, and he experienced Hawaiian culture as part of his day-to-day life. This was not the case several generations ago, as Mangauil remarks that his great grandmother was part of the generation that was punished for speaking Hawaiian. Turning to a more somber note, he mentions that he is also part of the first generation that can’t promise their children a future, referring to the current climate crisis. He compares the conflict on Maunakea to the current conflict between the Earth and human-caused climate change. Mangauil ends his presentation by emphasizing that we must do better for future generations.
The kia’i’s portion of the session was concluded with another ceremony led by Pua Case for acknowledging the information the audience had just received. The purpose was to leave astronomers with “kuleana” (responsibility). Case left the audience with a powerful statement: “We are not a camping trip on the mountain, we are not your luau, this is not a whim.” Case urged the audience to understand the land and know how you will impact it and its people before you come.
The next part of the session was led by two native Hawaiian astronomy graduate students, Makana Silva (The Ohio State University) and Tyler Trent (University of Arizona), who both indicated that they support the Thirty Meter Telescope project. Silva began by stating that as a native Hawaiian, his view and perspective were just as important as that of the kia’i, and that perspectives vary even amongst native Hawaiians. He explained that with the telescope, he can practice his culture today in a modern fashion and carry Hawaiian’s long-standing practice of astronomy into modern times. Silva also quoted the environmental impact statement and cultural impact statement, which claim that the Thirty Meter Telescope will not disturb the summit, but said he would reassess if other studies were to come forward. He concluded his statements by saying that “the Thirty Meter Telescope is something that Hawaiians can leave as a legacy for the next generation.”
Next, Trent outlined his perspective on the Thirty Meter Telescope project, primarily focusing on potential consequences if the project left Hawai`i. He lists the telescope’s scholarship fund for the advancement of children in Hawai`i and the workforce pipeline as notable ventures that would be lost. Trent also remarks that “astronomy gives Hawaiians an opportunity to advance economically” outside the other primary industries of tourism and the military. Additionally, the rejection of the Thirty Meter Telescope sheds a negative light on astronomy and acts as a symbolic rejection of astronomy.
For more information on this multifaceted issue, see our previous astrobites (here and here) and the links within them.
Press Conference: Cosmology & Exoplanets: Beyond the Nobel Prize (by Susanna Kohler)
This morning’s press conference was moderated by our very own Tarini Konchady, Astrobites author and AAS Media Fellow. Tarini introduced the panel’s topic — Cosmology & Exoplanets — with the explanation that the somewhat odd pairing was inspired by the split of the most recent Nobel Prize.
First up, Daniel Gilman opened with new work on how gravitational lensing is helping us to refine our understanding of dark matter. Different models of dark matter disagree: are the particles primarily “warm” or “cold”? These temperatures refer to the particles’ speed — and since warm particles move faster, they tend to wipe out small-scale structure. To determine which of these models is a better fit to our observations, Daniel Gilman (University of California, Los Angeles) and collaborators used the Hubble-observed gravitational lensing of distant quasars to hunt for evidence of small-scale dark-matter structure in the invisible halos of intervening galaxies. The team’s discovery of small clumps of dark matter has caused them to declare the warm dark matter picture unlikely, instead favoring the cold dark matter model. Press release
First up, Daniel Gilman tells us about how gravitational lensing is telling us about the nature of dark matter. #aas235pic.twitter.com/41afBteA4w
Each of these Hubble Space Telescope snapshots reveals four distorted images of a background quasar surrounding the central core of a foreground massive galaxy. [NASA, ESA, S.H. Suyu, and K.C. Wong]
What cosmology topic could be more controversial than dark matter? Geoff Chih-Fan Chen (University of California, Davis) leaps into the fray with a new measurement of the Hubble constant, a value that describes how fast the universe is expanding. There are two main ways of measuring the Hubble constant: one that uses supernovae and the distance ladder to measure the value locally, and one that uses the cosmic microwave background to measure the value in the early universe. The two approaches have found different values for H0, raising the question of whether this is just an error in one of the measurements, or if the tension is real and the value of H0 is actually different locally vs. in the early universe. By measuring the time delays of flickering variability in a gravitationally lensed quasar, Chen and collaborators were able to obtain an independent measurement of the Hubble constant in the local universe — and it matches up nicely with the previous measurements using supernovae. This further confirms the gulf between the two measurements of H0 and suggests a faster expansion rate in the local universe than in the early universe. Press release
We next transition to exoplanets, with Jason Wright (Penn State University) introducing NEID, an extreme-precision Doppler spectrograph that recently saw first light (see the cover image above). NEID (pronounced NOO-id) was installed on the 3.5-meter WIYN telescope at Kitt Peak National Observatory, and it will help us search for radial-velocity wobbles caused by the tug of planets on their host stars. NEID will have a precision roughly three times greater than previous generation state-of-the-art instruments, allowing us to detect wobbles of just 30 cm/s. For reference, the Sun’s wobble induced by Earth is about 10 cm/s, and Jupiter’s influence is around 1,200 cm/s. NEID is expected to start its main science mission this year. Press release
Ed Guinan says K dwarfs might be the Goldilocks star.
Last up, Edward F. Guinan (Villanova University) used a series of stellar surveys to sell us on K stars as the best target in the search for habitable exoplanets. These dwarfs — which are slightly cooler and less luminous than the Sun — have stable lifetimes of 15 to 50 billions of years (in comparison to our Sun’s ~10 billion years), giving planets plenty of time to evolve life forms. While K dwarfs aren’t as common as M dwarfs, they’re still more frequently found than Sun-like stars. And, importantly, they’re much less volatile than M dwarfs, which notoriously flare in high-energy emission. K-dwarf habitable zones are larger, which is another advantage relative to M dwarfs: for M dwarfs, “If you want to be warm, you have to be close — but you’re getting close to a nuclear power plant,” Guinan points out. K dwarfs might just be the Goldilocks star we want … so let’s go hunt some habitable planets! Press release
Special Session: New Horizons Results at 2014 MU69 (by Briley Lewis)
Alan Stern’s comparison of 2014 MU69 (Arrokoth) to Pluto’s mountains near Sputnik Planitia.
New Horizons PI Alan Stern started off with an overview of the mission. After its flyby of Pluto, the spacecraft was operational and ready to find a new target to further explore the outer solar system. Targeting MU69 was difficult, since it’s much smaller than Pluto (see image) and we were only able to observe about 1% of its orbit before flyby. It’s a cold classical KBO, meaning it was born at its current distance from the Sun and has low eccentricity and inclination. It’s about 33 km long, and it looks like two disks smushed together, known as a contact binary. Learning more about MU69 can tell us about how it formed, which in turn gives information on the conditions of the early solar system.
But before we talk about MU69, Marc Buie tells us about how we got the spacecraft there in the first place. To find a new destination, there was a lot of searching, including massive campaigns with ground-based telescopes to look for occultations, where the KBO passes in front of a distant star, giving us information on its size and shape based on the starlight it blocks out in transit. The team led multiple campaigns — spread through South Africa, Argentina, and even on the SOFIA airplane-based observatory — and got enough observations to narrow down their predictions on the shape and ensure the spacecraft would be in the right place for the flyby.
The bi-lobed object MU69, as captured by NASA’s New Horizons spacecraft during its flyby. [NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute]
The rest of the session focused on specifics on what we’ve learned about MU69 from the New Horizons data, and how that all ties together to paint a picture of how it formed. Alissa Earle tells us that the color of MU69’s two lobes is pretty much the same, and it’s consistent with other cold classical KBOs. Since the two lobes are similar, this implies they formed close to each other and then came together slowly. John Spencer noted how the two flattened lobes are remarkably aligned at their equators — unlikely to be a coincidence! Instead, these two lobes probably formed from a rotating clump due to streaming instabilities (a known mechanism in planet formation) and their alignment is a natural consequence of their orbital motion. (On a slightly related note, Spencer also searched near MU69 for rings or satellites — nothing so far!) Orkan Umurhan gave us some additional information on MU69’s properties: a temperature ranging from 16–55 K (very cold!) and a mean density of around 0.45 g/cm3 (less dense than liquid water). Lastly, Kelsi Singer looked at the craters on MU69 and what they can show us about its past. There are very few small craters on its surface, meaning there aren’t that many small KBOs to create those craters — but what does this mean for the Kuiper Belt? Either not that many small objects are made in the outer solar system, or they’re made and then somehow destroyed. Hierarchical accretion would likely lead to many small objects, and gravitational collapse would lead to few.
All signs point to a “gentle” merger leading to the contact binary, since if the two lobes were moving faster than 2.5 meters per second, they would have destroyed or significantly altered each other on impact. These slow collision speeds (and other evidence, like Singer’s cratering results) point to cloud collapse instead of hierarchical accretion for how planetesimals form — an important result for planet formation!
Plenary Lecture: The Future of Infrared Astronomy in the Context of Spitzer, SOFIA, and JWST (by Briley Lewis)
Peter Eisenhardt with a temperature map of an exoplanet from Spitzer.
Spitzer is nearing its last days — the famous infrared satellite is shutting down at the end of the month, January 30th, 2020. Peter Eisenhardt (JPL) takes us on a tour of Spitzer’s greatest hits, illustrating the telescope’s lasting legacy. He tackles three main questions through the lens of Spitzer observations: where did we come from, how did the universe evolve, and are we alone?
For almost 17 years, Spitzer has been observing the infrared sky, peering into distant galaxies to answer those first two questions. It has estimated the rate at which stars form over the history of the universe, and also the mass density of those stars, giving us an idea of how the universe has changed over time. Spitzer has also provided great information on exoplanets, trying to answer the fundamental question of our place in the universe; it created the first exoplanet phase curve and temperature map, and was essential to the confirmation of the famous TRAPPIST-1 system.
Now, it’s spending its last days observing distant galaxies as part of a precursor survey, providing important context on where JWST and other future missions should point to see the early universe. It has also already observed many of the planets planned for early JWST observations, paving the way for the success of these future studies.
James De Buizer discussing SOFIA (and claiming his title of “tallest astronomer”).
Next, James De Buizer (SOFIA Science Center) told us about SOFIA, the only far infrared observatory available for astronomy until the proposed Origins Space Telescope, planned tentatively for the 2030s if selected by the decadal survey. This unique facility — a telescope on an aircraft — flies up above the parts of the atmosphere that block far-IR light. Since SOFIA isn’t in orbit, it’s easily serviceable and upgradable, making it a flexible and powerful resource for infrared astronomy.
It’s already made numerous important contributions to astronomy: observations of the galactic center, mapping of star formation in the Orion Nebula, information on the importance of galactic outflows in the intergalactic medium (all the stuff between galaxies), and signatures of helium hydride, a tracker of how molecular hydrogen formed before there was enough dust in the early universe. De Buizer emphasizes that this is the only far infrared observatory that we’ll have access to for the next few years, making it absolutely integral to other upcoming missions such as JWST. There’s a lot SOFIA will be able to do to complement the science done by other new observatories!
SOFIA, a modified Boeing 747SP carrying a 2.7-m telescope. [NASA]
Newton Lacy Pierce Prize: Life and Times of the Lowest Mass Galaxies (by Mia de los Reyes)
As #AAS235 began winding down, Daniel R. Weisz (University of California, Berkeley) gave the second-to-last plenary of the day. After discussing the importance of dwarf galaxies and the many astrophysical questions they can be used to answer, Weisz focused on dwarf galaxies as tools for “near-field” cosmology. Nearby dwarf galaxies are analogs to the lowest-mass galaxies at high redshifts, and they can shed light on some of the events that happened in the early universe.
NGC 147, a dwarf spheroidal galaxy in the Local Group. [Ole Nielsen]
Weisz began by describing how resolved stellar populations can be used to measure star formation histories of dwarf galaxies. To do this, we plot where individual stars fall on a color–magnitude diagram; by fitting this plot with models, we can estimate when galaxies formed most of their stars. The Hubble Space Telescope has revolutionized this game with its high angular resolution, which allows us to resolve many more individual stars in nearby dwarf galaxies. In 2014, Weisz’s group published a study using archival HST data to get star formation histories of 40 local dwarfs — the largest sample to date!
With these data, Weisz’s group aimed to investigate the link between dwarf galaxies and reionization, the epoch in the universe when the neutral universe was ionized by high-energy UV photons. First, Weisz asked how dwarf galaxies were affected by reionization. By seeing what dwarf galaxies’ star formation histories looked like before and after the epoch of reionization (which lasted roughly between redshifts 6–10), his group showed that reionization quenched star formation in the lowest-mass objects, called “ultra faint dwarf” galaxies.
Did reionization ionize ultra faint dwarfs at the time, ceasing star formation?
Weisz then asked how dwarf galaxies might contribute to reionization. From the star formation histories of dwarf galaxies, one can estimate how the ultraviolet luminosity of dwarf galaxies changed over time. Weisz’s group used this to figure out how much dwarf galaxies — in particular, the “ultra-faint dwarfs,” which are expected to be extremely common — would have contributed to reionization.
It turns out that ultra-faint dwarf galaxies must have been rarer than expected, otherwise they actually contribute too many high-energy photons to explain our observations of reionization! In the future, the James Webb Space Telescope will allow us to check this directly by actually doing a statistical census of the number of ultra-faint dwarf galaxies.
However, all of these results are based on observations of the dwarf galaxies around the Milky Way. Are these Milky Way satellites truly representative of all dwarf galaxies? “The natural place to answer this question is M31,” according to Weisz, since it’s the nearest system of satellite galaxies. He compared the star formation histories of Milky Way satellites with those of M31’s satellites, and preliminary results seem to show some differences! Around the Milky Way, ultra-faint dwarfs “quench” (finish most of their star formation) very early, while more luminous galaxies quench late. In the M31 system, none of the dwarf galaxy satellites quench quite as early as the Milky Way galaxies; most of them actually quench at intermediate times! These suggest that the Milky Way system is unique, and that studying the Milky Way satellites alone might give us a biased view of dwarf galaxies.
More data are needed to answer these questions. Weisz is leading an ongoing project to obtain more data from HST. In the future, hopefully we’ll be able to study more distant galaxies. JWST — and next-generation larger space telescopes — will enable measurements of individual stars in galaxies at further distances, letting us test if dwarf galaxies in our Local Group (of which M31 and the Milky Way are the two biggest galaxies) are unique.
Lancelot M. Berkeley Prize: The Event Horizon Telescope: Imaging a Black Hole (by Briley Lewis)
One of the biggest science events of this year was the first image of a black hole. Sheperd Doeleman (Center for Astrophysics | Harvard & Smithsonian) represented the Event Horizon Telescope (EHT) team today to talk about the journey to that amazing first image of a black hole, and where EHT is going in the future.
Eight stations of the EHT 2017 campaign over six geographic locations. [EHT Collaboration et al 2019]
The size and shape of a black hole’s shadow encodes lots of information, including effects of general relativity. The most obvious choice for a target to look at is Sgr A*, the central black hole of our Milky Way. It’s 4 million times the mass of the Sun, and trying to see its shadow is the same as trying to see a grapefruit on the moon. Scientists figured out that if you’re observing in the radio, you’d need a baseline about the size of Earth itself to resolve this, and thus the EHT was born.
The team took existing radio telescopes all around Earth — even at the South Pole — and added technology to them, such as extremely precise hydrogen maser clocks, to link them together into one powerful instrument and achieve this goal. This Earth-sized telescope uses the idea of very long baseline interferometry (VLBI) and produces so much data that the fastest way to transfer all of it is by flying a bunch of hard drives somewhere in an airplane. Once they had their first data, the EHT team divided into four groups to analyze the data, in an effort to avoid human bias. They all came up with remarkably similar images, showing good agreement on the basic structure of the shadow of the black hole in a different galaxy, M87.
The first image of a black hole, from the plenary by Sheperd Doeleman.
So, what did they find in this first black hole observation? M87’s black hole is huge, around 6 billion times the mass of the Sun. Also, it looks like the spin of the black hole is comparatively unimportant to the features we see, but the metric used for general relativity is very important.
Looking to the future, adding more telescopes will lead to better images. Doeleman calls this the “ngEHT” (next generation EHT). The near future goals include: adding three new stations (Greenland, Kitt Peak, and NOEMA), looking at the polarization of M87, imaging our very own Sgr A*, and adding even more telescopes beyond the already planned three. By the end of the decade, he hopes to have better angular resolution and dynamic range, with the goal of imaging and understanding the connection between a black hole and its jets.
Given that Sgr A* is so nearby, and such an interesting target for our studies of the galactic center, why hasn’t the team imaged it yet? Sgr A* is variable on much smaller timescales than M87, which presents difficulties considering the EHT has to wait for the Earth to rotate to get more baseline coverage from the telescopes. Someday telescopes in low Earth orbit could solve this problem, making time-domain movies of black hole variability.
This first image of a black hole has been an international sensation, and Doeleman doesn’t underestimate the effect his team’s work has had; the image has been seen by 4 billion people, and now he’s trying to use their success to bring the public into science. This has been a huge collaborative effort, too, with 250 team members spread across 60 institutes and 20 countries. As Doleman says, “If you want to go far, go together. To work on the biggest questions and succeed is indescribable … and we are not done yet.”
Editor’s Note: This week we’re at the 235th AAS Meeting in Honolulu, HI. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume the week of January 20th.
Dannie Heineman Prize: Making a Habitable Planet (by Ellis Avallone)
Prof. Ted Bergin from the University of Michigan discusses the required ingredients for a habitable world.
This morning started off with Edwin (Ted) Bergin (University of Michigan), the winner of this year’s Dannie Heineman Prize, discussing the formation of habitable worlds. He began by thanking all of his collaborators, placing special emphasis on the students who had “taught [him]so much” and the band Rush that “helped [him]survive grad school.” Bergin began his talk by highlighting some of the diversity work he’s been involved in, a notable venture being a workshop at the University of Michigan to discuss the effects of unconscious bias in the faculty hiring process and how to work against these biases.
Bergin then moved on to the main focus of the talk, carbon — specifically its journey from the molecular cloud the Sun was born in to present day Earth. He then introduced the required ingredients for a habitable world like Earth:
The planet must be rocky.
The planet must be the correct distance from its host star for liquid water to exist.
The elements that are essential for life must exist on that planet (e.g. carbon, oxygen, water, and nitrogen).
Although these ingredients exist on Earth, there are a few things that should be emphasized. To start, water makes up only 0.05% of the total mass of Earth. Next, Earth is a carbon-poor planet, even though carbon is an essential ingredient for life. The inner solar system is also carbon-depleted, while comets from the outer solar system contain excesses of carbon. Even with these deficiencies, life still exists! Astronomers would like to know whether this is a common outcome for other worlds.
To answer this, Bergin looks to the formation of our solar system, tracing the evolution of carbon from the early Sun to where we are now. All stars are born in molecular clouds, large clouds of gas that, when disturbed, can condense to form stars. These molecular clouds contain many simple molecules and hydrocarbons, which are the primary carriers of carbon in molecular clouds. As a stellar core forms, an ice mantle builds up. This mantle provides ices to the star’s protoplanetary disk, which forms after stellar winds remove much of the gas that encloses the star.
Artist’s illustration of a protoplanetary disk surrounding a young star. [NASA/JPL-Caltech]
Bergin then transitions to discussing what happens to carbon at various distances from the star. Comets, for example, can only carry carbon to the inner solar system if they form outside the snowline, the region in the solar system where ices can form. Carbon-containing rocks, however, can form within 1 AU of the Sun. “I’ve just proved to you that Earth is made of rocks,” Bergin explains.
Why does this seemingly trivial concept matter? It’s important to understand how Earth got its specific carbon abundance when it formed. As mentioned previously, the inner solar system is depleted of carbon while the outer solar system contains excess carbon. As Jupiter’s core formed, it created a gap in the planet-forming disk that disconnected the inner solar system from the outer solar system. Earth’s carbon content requires that this gap formed within the first million years of the solar system. However, within this strict requirement for Earth’s carbon, it remains unclear how often this happens for other planetary systems. Future missions like the Origins Space Telescope may help solve the mystery of how our habitable world came to be.
Press Conference: The Milky Way Inside & Out (by Kate Storey-Fisher)
The Radcliffe Wave, a newly detected sinusoidal feature in our local galactic neighborhood. [Alyssa Goodman/Harvard University]
This press conference brought us insights from our home neighborhood in the Milky Way. Alyssa Goodman (Center for Astrophysics | Harvard & Smithsonian) started us off with the discovery of the Radcliffe Wave, a previously undetected sinusoidal structure of star-forming gas not far from our solar system. The wave was found thanks to new precisely measured distance data, calculated using proper motion observations of masers and a 3D dust map of the galaxy. These revealed a feature 9,000 light-years long and 400 light-years wide, which has a damped sine-wave shape unlike anything we’ve seen. Dubbed the Radcliffe Wave, after the Radcliffe Institute at Harvard where the discovery was made and to honor the early women astronomers who worked there, the feature could indicate a collision in our galactic neighborhood or even hint at the influence of dark matter. Press release
Next, James De Buizer and Wanggi Lim (Stratospheric Observatory for Infrared Astronomy [SOFIA] / Universities Space Research Association) announced a newly uncovered population of stars in the Swan Nebula (see cover image). Using the SOFIA telescope on board a Boeing 747, the team obtained the highest resolution infrared image ever taken of the nebula, which is in the Sagittarius constellation 5,000 lightyears away. This revealed a population of young and very massive stars, which are rare but crucial to the story of galaxy evolution. The new observations also show that the nebula has undergone multiple eras of star formation, with regions of older stars as well as younger stars, giving us a detailed understanding of how the Swan Nebula hatched over its lifetime. Press release
A young star cluster, Price-Whelan 1, is the first to be discovered in the Magellanic Stream. [D. Nidever; NASA]
Adrian Price-Whelan (Flatiron Institute) continued the theme of new star populations with the discovery of a young cluster on the outskirts of the Milky Way halo. By mining the 1.7 billion precise distances and proper motions in the Gaia DR2 catalog, Price-Whelan found a cluster of stars with correlated distances and motions indicating a bound system. The cluster is a young 116 million years old and is small at 1,200 solar masses — typical parameters for star clusters in the Milky Way disk. However, the data showed that it is a whopping 94,000 lightyears away, and it’s far from the midplane of the disk. Because of the cluster’s young age, it wouldn’t have had time to migrate there from elsewhere, and the only potential star-forming regions out there are the gas stream between the Large and Small Magellanic clouds. This means that Price-Whelan 1, as the cluster is called, is the first detected star cluster in the Magellanic Stream. Press release
A cluster this exciting deserves more data. David Nidever (Montana State University) discussed the spectroscopic follow-up he performed on the Price-Whelan 1 star cluster. He found an age consistent with that reported by Price-Whelan, and a heavy element content 6% that of the Sun’s, which is consistent with the known content in the leading arm of the Magellanic Stream. Furthermore, the mean radial velocity of the stars clocks in at a speedy 277 km/s, also matching the velocity of the leading arm. These results give high confidence that the cluster was born in the Magellanic Stream — and this in turn tells us the distance to the stream’s leading arm, which must be twice as close as previously thought. This suggests that the Magellanic Stream will merge with the Milky Way sooner than expected, replenishing our gas reservoir.
Plenary Lecture: Fast Radio Bursts (by Aaron Tohuvavohu)
In this explosive plenary, Dr. Jason Hessels (ASTRON & University of Amsterdam) began by telling the story of fast radio bursts (FRBs) in parallel with the narrative of discovery surrounding gamma-ray bursts (GRBs); phenomenologically somewhat similar events, discovered 40 years earlier, and on the opposite side of the electromagnetic spectrum.
Artist’s impression of a fast radio burst observed by the Parkes Radio Telescope. [Swinburne Astronomy Productions]
In contrast to GRBs, the FRB field was hindered for a long time due to the lack of wide-field monitors, and there were multiple years between the first detection of this phenomenon (in 2007) and further detections. In further contrast, while GRBs are intrinsically rare events (happening at most once per day in the observable universe), there is a potentially observable FRB every 10 seconds! Hessels further described that, unlike gamma rays, which travel essentially undisturbed from their source, FRBs are dispersed, scintillated, and scattered, and they have measurable Faraday rotations. While these effects can be impediments to measuring and finding FRBs, they are also extremely useful in probing the characteristics of the cosmos that the FRB encounters on its journey from source to our detector. The dispersion measure probes the integrated electron density along the line of sight, the scintillation and scattering probes the “clumpiness” of the material the FRB passes through, and the rotation measure allows astronomers to measure and map the strength of the magnetic fields along the line of sight.
Hessels continued the scientific discovery narrative in parallel with the history of GRBs. The localization of GRBs to their respective host galaxies, and the characterization of those hosts, was critical in determining the progenitors of GRBs and their diversity. Similarly, the discovery of repeating FRBs, which can be localized sufficiently for host-galaxy identification, was a dramatic transformation for the field. This simultaneously ruled out so-called ‘cataclysmic progenitors’ for those repeaters, but it also opened up the avenue for localizations — which rapidly followed with interferometric instruments. Hessels argued that localizations are useful not only for understanding what the progenitors of FRBs are, but also for using FRBs as efficient probes, even if we are ignorant as to the actual physical emission mechanisms.
Hessels concluded by reminding the audience that FRBs are good for (at least) three things: as probes of extreme environments, as a possible new type of astrophysical object, and as probes of the intervening material. The future is (radio) bright for the field of FRBs, with large-field-of-view survey instruments (such as CHIME) now online and more instruments planned in the near future. This author hopes that FRBs break from the GRB narrative in the duration between discovery and identification of the progenitors (30–40 years for GRBs!), but regardless: a very exciting decade of fast radio bursts lies ahead.
RAS Gold Medal Lecture: Star Formation and Galaxy Evolution Through the Lens of a Scaling Law (by Ellis Avallone)
The next talk of the day was by the winner of the RAS Gold Medal, one of the highest awards in astronomy, Rob Kennicutt (University of Arizona). Rob is an expert in star formation, and has had a long career in understanding various facets of this process. The talk began with a tribute to the late Dr. Paul Hodge, Kennicutt’s thesis advisor and a giant in astronomy.
Kennicutt then moved into discussing his career focus: star formation in galaxies. This field falls at the intersection of the disciplines of star formation and galactic evolution, exploring the ways in which these processes are intertwined. As if this weren’t already complicated enough, understanding star formation in galaxies is made even more difficult by the diversity of phenomena that occur in galaxies and the complex physics underlying these various processes.
The spiral galaxy NGC 1559, pictured in this Hubble image, provides an excellent example of star formation in a nearby galaxy. [NASA/ESA/Hubble]
But have no fear! A ton of progress has been made within the past several decades in understanding different facets of star formation. A primary focus of Kennicutt’s talk was the dependence of star formation rate surface density on gas surface density. This connection was made abundantly clear by the advent of multi-wavelength observations in the 1990s. As observations improved and more galaxies were studied, two regimes of star formation started to come forward: one where star formation is largely driven by gravitational processes and another where star formation is driven by the formation of molecular gas. This disparity was explained by invoking a third regime of star formation that occurred only in regions with a high gas surface density. Even with these disparities, a tight correlation between gas surface density and star formation rate surface density persists as data continues to improve.
Kennicutt concluded his talk by discussing some future goals in the study of star formation in galaxies. If the goal is to create recipes for star formation models, the various dependencies of star formation on other factors are extremely powerful. However, if the goal is to understand the underlying physics of star formation, then we have to find a few more pieces of the puzzle to fully grasp what’s going on. Kennicutt ended with a quote from his colleague Dr. Martin Rees, who said “star formation is a bit like the weather,” in that it is a highly complex interconnected system. It’ll be interesting to see what advancements this field makes in the coming years.
Plenary Lecture: Twinkle Twinkle Little Star, Now I Know What You Are (by Tarini Konchady)
The last plenary of the day was given by Jennifer van Saders (University of Hawaii). Her talk was on gyrochronology, the estimation of a star’s age from its rotational period. Van Saders began by laying out how stellar studies had been advanced by missions like Kepler and the Transiting Exoplanet Survey Satellite. These missions have provided astronomers with data that were heretofore unprecedented in their frequency and precision. By being able to observe stars precisely on short timescales, we’ve become aware of the many small variations that stars experience.
Stars in the open star cluster NGC 3766. [ESO]
Van Saders focused on stellar rotation in particular. In the first part of her talk, she discussed how open star clusters of different ages could show us that the period of rotation of a star changes with time. Stars in older clusters tend to rotate more slowly than stars in younger clusters, and hotter stars slow faster than cooler stars.
However, as handy as these relations are, they aren’t enough to explain the bulk of the stars we know of. Stars like our Sun don’t follow these rotation–age–temperature relations very well. Van Saders explained how this discrepancy was noticed through asteroseismology (the study of stellar oscillations), another field of study enabled by missions like Kepler. Asteroseismology offers a very accurate age determination of stars, and these ages for Sun-like stars didn’t agree with the ages derived from rotation-based models.
While the discrepancy could be due to observational bias, Van Saders opted to re-examine the rotation–age model. This involved incorporating something called the Rossby number — the ratio between rotational period and the timescale for convective processes to occur within the star. By using the Rossby number to set the time at which the braking of a star’s rotation slowed down (meaning that past that point the star’s rotation was faster than models without the Rossby number predicted), the rotation–age relation more closely matched the asteroseismology inferences. However, the modified relation still isn’t completely reliable for ages.
Van Saders concluded her talk by noting that the Sun — which forms the baseline for many models — might be transitioning in its rotational period. There is a lot of parameter space that hasn’t been probed regarding rotation–temperature–age relations, but fortunately there are a lot of astronomers on the job!
Stellar age versus stellar mass with the knowledge of the rotation-age relation highlighted for the appropriate regions.
Editor’s Note: This week we’re at the 235th AAS Meeting in Honolulu, HI. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume the week of January 20th.
AAS Prize Presentations and Plenary Lecture: The Role of Feedback in the Evolution of Galaxies (by Ellis Avallone)
This morning started off with Megan Donahue (Michigan State University) awarding AAS prizes. To read more about the prizes and their winners look out for a press release by AAS later this week!
Next, Tim Heckman (Johns Hopkins University) discussed where we’re at in understanding galaxy evolution. Heckman began by introducing this topic through the lens of cosmology. “We’re in the era of precision cosmology.” Because of this, we now have a very good understanding of the evolution of dark matter haloes that surround galaxies as they form and grow. However, we still don’t understand much of the underlying physics that’s involved in the current model of galactic evolution, in which galaxies grow primarily through a series of merger events. This is further complicated by current numerical models, which cannot reach the resolution needed to resolve these physical processes.
High-speed jets emitted from around supermassive black holes are one type of feedback that can affect galaxy evolution. [ESA/Hubble, L. Calçada (ESO)]
To address these outstanding uncertainties, Heckman focused on the role of feedback in galaxy evolution — the process by which energetic events like supernovae and active galactic nuclei affect the growth of galaxies. Galaxy feedback affects high-mass and low-mass galaxies differently. Low-mass galaxies are the most susceptible to stellar feedback, while feedback in high-mass galaxies is primarily driven by supermassive black hole activity. Heckman concluded this talk by discussing where feedback primarily influences galaxy evolution. Recent studies have determined that galaxies are most influenced by feedback in the circumgalactic medium. However, more observations need to be done to improve current simulations and uncover the mysteries of galaxy evolution.
Workshop: Science Communication Through the Lens of Astrobites (by Kate Storey-Fisher and Briley Lewis)
Astrobites authors Briley Lewis and Kate Storey-Fisher led today’s workshop (and had a lot of fun doing so!).
Today we had the chance to bring more Astrobites to AAS through our workshop “Science communication through the lens of Astrobites” led by Astrobites authors Kate Storey-Fisher and Briley Lewis.
So, what makes an Astrobite? We started today’s workshop by discussing two main topics in science communication: language and storytelling. Language choices are particularly important in science writing, since we need to be careful about what jargon we use; deciding which words are appropriate for an article depends entirely on knowing your audience (who they are, why they care, what they already know). Storytelling is also important because it keeps your reader interested, and helps make the information memorable. Basic narrative structures (such as “and, but, therefore”) are great starting places for constructing the story of your science.
Workshop participants analyzing an abstract to write an Astrobites-style article.
After a crash course in these fundamentals of science writing, we set our participants out to write an introduction to their very own Astrobite. Participants came up with compelling intros, steering clear of jargon and incorporating a narrative hook, and then engaged in peer editing and analysis of published Astrobites to improve their drafts. Overall, there was a lot of great discussion on the value of making science accessible, and how to actually accomplish that goal!
Participants were encouraged to write and submit guest posts to Astrobites — if you have a pitch, you can contact us here to submit one! If you’ve been walking around the posters at the exhibit hall, you may have noticed that we also accept undergraduate research submissions, which can be submitted here.
Press Conference: Things That Go Bump in the Night (by Susanna Kohler)
AAS Press Officer Rick Fienberg opened the first press conference of the day with “I think this is the most people I’ve ever fit up on this stage,” introducing the six speakers who were going to tell us about a variety of transient sources.
The Livingston LIGO facility, which recently made the first single-detector gravitational-wave event detection. [Caltech/MIT/LIGO Lab]
What’s the latest from the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo, its European counterpart? Katerina Chatziioannou (Flatiron Institute) announced the biggest news yet from the LIGO-Virgo O3 observing run: we’ve discovered gravitational waves from another binary neutron star pair, GW190425, and the pair combined weighs between 3.3 and 3.7 solar masses. This is heavier than any other known binary neutron star system — the largest known in our galaxy has a combined mass of 2.9 solar masses — and challenges theories of how these binaries form. Fun fact: this is also the first event identified via data from the LIGO Livingston detector alone, rather than via combined data from the LIGO Livingston and the LIGO Hanford detectors. Even with only one detector online at the time, the signal was strong enough for the team to be able to make an unambiguous detection. Press release
The location of FRB 180916 is in a galaxy’s spiral arm, marked with a green circle in this image from the Gemini-North telescope. [NSF’s Optical-Infrared Astronomy Research Laboratory/Gemini Observatory/AURA]
One type of transient source that has especially baffled astronomers is the fast radio burst (FRB) — an extremely bright flash of radio waves of extragalactic origin that lasts only a few milliseconds. We’ve detected about 100 of these, and we think they’re very common, occurring possibly once every 10 seconds across the whole sky. We’re not yet sure what causes an FRB — and the first step to solving this mystery is to localize FRBs, i.e., determine where they originated from. Benito Marcote (Joint Institute for VLBI ERIC [JIVE]) & Kenzie Nimmo (ASTRON & University of Amsterdam) presented on new work using the European VLBI Network (EVN) to localize a repeating burst, FRB 180916.J0158+65, to a star-forming arm of a spiral galaxy located 500 million light-years from Earth. This is just the second time we’ve ever localized an FRB, and FRB 180916.J0158+65 is by far the closest source we’ve pinned down. Perhaps we’ll be able to use it to better understand these mysterious, energetic flashes! Press release
Chandra X-ray images reveal the motions of knots within M87’s jet. [NASA/CXC/SAO/B. Snios et al.]
Can’t get enough of the supermassive black hole in M87, the monster we recently imaged with the Event Horizon Telescope? Ralph Kraft (Center for Astrophysics) gives us more news to chew on from this famous black hole, in the form of recent Chandra X-ray observations of the powerful jets spewing from its poles. The observations allow us to measure the velocities of knots moving within the jet pointed closest to us; by de-projecting these motions, we can determine the speed of the underlying flow of the jet. These new measurements provide the first direct evidence that matter in the jet moves at relativistic speeds of more than 99% the speed of light. They also reveal useful information about the physics of jets like this one that commonly accompany active supermassive black holes. Press release
Switching gears, Thomas Fauchez (NASA Goddard Space Flight Center) presented on a new technique we can use to detect oxygen in the atmospheres of exoplanets, potentially advancing the search for life beyond the solar system. Oxygen levels similar to Earth’s were previously thought to be too faint to detect on exoplanets, but Fauchez and collaborators conducted simulations showing that an absorption feature at the infrared wavelength of 6.4 µm could give away the presence of oxygen in a planet’s atmosphere — and therefore possibly point to habitability of the world. They show that this feature could be detected in the spectra of nearby planets when observed with the upcoming James Webb Space Telescope. Press release
V Sagittae is predicted to merge within the next century.
Last up, Bradley Schaefer (Louisiana State University) opened with his exciting punchline: the binary star V Sagittae, which consists of a white dwarf fed by material from an ordinary star, is inspiraling ever more rapidly and is on course for a collision. Schaefer and collaborators’ best estimates suggest the binary will likely merge soon: in the year 2083, give or take 16 years. As it collides, the system will become as bright as Sirius or even possibly Venus — appearing as a guest star in our sky that will last roughly a month near peak brightness. Mark your calendars! Press release
Helen B. Warner Prize: Not Your Grandparents’ Galaxy: The Milky Way in the Era of Large Surveys (by Mia de los Reyes)
Jo Bovy (University of Toronto) started his plenary talk with a goal: “I want to take you on a journey through the Milky Way,” he said. He listed all the main visible parts of the Milky Way — the disk, the bulge, and the stellar halo — and explained how there are still some big open questions about the MIlky Way’s structure. How did all of these components form and evolve? Perhaps more importantly, how do they all fit together?
We’ve made a lot of strides towards answering these questions in the last decade. “The big difference between now and ten years ago,” said Bovy, are large surveys. Bigger is better when it comes to Milky Way surveys — and we’ve gotten a lot better. For example, we’ve obtained high-resolution spectra of thousands of stars using surveys like SDSS APOGEE, and positions and velocities for 1.7 billion stars with the Gaia satellite.
What have we learned from these large data sets so far? Bovy laid out several of the main results in galactic studies over the past decade, focusing on the different components of the Milky Way. For example, chemical evolution patterns in the Milky Way’s disk indicate that the early disk was extremely uniform, thick, and turbulent — but that it cooled and became thin and chemically stratified (i.e. having more metal-poor stars near the outskirts) at later times. After this thin disk formed, radial mixing processes began to churn the disk, perturbing it and producing transient spiral patterns.
Artist’s impression of the Milky Way, showing its three main visible components: the disk, the halo, and the bulge. [ESA]
Meanwhile, chemical abundances have also been used to confirm that the stellar halo (the large spheroidal blob of stars surrounding the entire galaxy) is mostly made up of old stars from accreted dwarf galaxies. Some evidence has suggested that some stars in the stellar halo might also come from the disk, which could have been “puffed up” after a major merger event (like the so-called “Gaia Sausage”). However, using the combined power of large datasets from APOGEE and Gaia, further work shows that this merger may not have been so major — the merging object was likely less than one-tenth the mass of the Milky Way — and is unlikely to have puffed up the disk.
Finally, Bovy described the galactic bulge. Although all galaxies have bulges of some kind, only since 1990 or so have we known that the Milky Way has a bar at its center. The bar is chemically similar to the early Milky Way disk and likely formed ~8 Gyr ago from the disk. Bovy showed how the rotation of the bar can be measured using Gaia data, and how the bar has likely just been rotating steadily since its formation.
Bovy then explained how all these results come together to support a single picture of Milky Way evolution — one mostly dominated by internal processes, rather than external processes like major mergers. Bovy ended his plenary talk by pointing out that it’s important for surveys to not only be large but also open and accessible to scientists worldwide. Open data is good for both science and for scientists, so we should all “urge the people in charge to make sure data is fully open!”
Press Conference: TESS Explores Exoplanets & More (by Susanna Kohler)
Artist’s illustration of NASA’s TESS mission observing a system of transiting exoplanets. [MIT]
Paul Hertz, astrophysics division director at NASA Headquarters in Washington, reminds us that just 20 years ago, we didn’t know whether exoplanets were common or rare. Now, we know that nearly every star in the galaxy has exoplanets — and the Transiting Exoplanet Survey Satellite (TESS) has already discovered thousands of these planet candidates in just the first year and a half since its launch. What are some of the latest results coming from this promising mission?
The first three presentations of this press conference focused on a major new discovery — the compact multi-planet system TOI 700. Emily Gilbert (University of Chicago) introduced the cool M dwarf located just over 100 light-years away and its newly found planets:
TOI 700b, an Earth-size, likely rocky planet on a 10-day orbit
TOI 700c, a larger, likely gaseous planet on an 16-day orbit … and (drumroll, please) …
TOI 700d, TESS’s first discovery of a roughly Earth-size transiting planet that, with an orbit of 37 days, lies in its host’s habitable zone.
How did we confirm TOI 700d? It seems fitting that, with just a month of observations left before the Spitzer telescope is retired, this venerable spacecraft was the one to detect transits from TOI 700d and confirm TESS’s first Earth-size habitable-zone planet. Joseph Rodriguez (Center for Astrophysics | Harvard & Smithsonian) reported the observations, as well as some ground-based observations further characterizing TOI 700c.
The three planets of the TOI 700 system. [NASA Goddard SFC]
Lastly, Gabrielle Engelmann-Suissa (NASA Goddard Space Flight Center) presented new 3D climate modeling that explores the potential atmosphere of TOI 700d, a tidally locked planet (i.e., the same side of it always faces the star). A number of outcomes are possible — from an ocean-covered world with a dense atmosphere, to a cloudless, all-land version of modern Earth. Eventually, we hope to be able to measure spectra of TOI 700d that we can then compare to the simulated spectra produced by Engelmann-Suissa and collaborators to better understand this planet. Joint press release on TOI 700
TOI 1338 b, silhouetted by its two host stars. [NASA Goddard SFC/Chris Smith]
Next, Veselin Kostov (NASA Goddard Space Flight Center) presented on TOI 1338, the first circumbinary planet detected by TESS. The planet was discovered in TESS data by Wolf Cukier, a high schooler and summer intern at Nasa Goddard SFC at the time. TOI 1338 lies about 1,300 light-years away, and the two stars of the binary orbit each other once every 15 days. The planet was difficult to spot due to its irregular orbit — between 93 and 95 days — and variable depth and duration; this unusual behavior is due to the orbital motion of its host stars. Press release
Rounding out the session, Angela Kochoska (Villanova University) presented on the binary star Alpha Draconis — the star that, 4,700 years of precession ago when the first pyramids were built in Egypt, had Polaris’s place as the star closest to the north rotational pole of the Earth. Despite being a very well-studied, naked-eye star, Alpha Draconis has only just been discovered to be eclipsing. TESS data revealed the brief eclipses that had been missed by ground-based observations in the past, providing us with a wealth of new information we can use to study this system and analyze its properties. These results demonstrate that TESS is useful not only for exoplanet science, but also for stellar science as well! Press release
Plenary Lecture: The Stewardship of Maunakea’s Legacy from the Perspective of the Hawaiian and Astronomical Communities (by Briley Lewis)
Amy Kalili (‘Ōiwi TV), indigenous language advocate, introduced a perspective on the stewardship of Mauna Kea rooted in the language and culture of Hawaiian communities. Her task today was not to definitively give an answer to the conflict surrounding astronomy on the mauna, but to prompt new thoughts and discussions between the stakeholders involved.
Mauna Kea, as viewed from Mauna Loa Observatory. [Nula666]
Kalili introduced the idea of “‘imi pono” (seeking in a beneficial manner) vs. “pono ‘imi” (doing something just to get it done), applying this concept to the interactions between astronomers and the Hawaiian communities. We need to consider if the 13 telescopes on Mauna Kea are ‘imi pono or pono ‘imi, and what direct benefits our science and discoveries have to the surrounding communities and those outside of astronomy. She also stresses that this is not a debate on science versus culture; though there have been misconceptions and misrepresentations of Hawaiian views on science, she explains that “we as Hawaiians embrace and embody ‘imi,” such as through the art of celestial navigation and kilo hōkū (observing the stars). Hawaiians and astronomers have “a common aloha for the art and science of astronomy”, but the threshold for what science is “worth it” differs based on context and kuana’ike (perspective).
Looking forward, her major takeaway is that there is a significant need for greater pilina (relationship building) and ho’oka’a’ike (communication). Pilina is a requisite to build trust, and it takes “time, energy, sincerity, and long-term commitment.” However, it doesn’t mean we have to agree on everything, just that we need to engage with respect. Ho’oka’a’ike engages multiple audiences and voices, especially those that previously may not have had a seat at the table, and prioritizes ho’olohe (listening) over wala’au (talking).
Kalili’s question for those attending this meeting is this: How can we, as astronomers/experts in the field, contribute to pilina, ho’oka’a’ike, and kālailai (analysis/assessment) with regards to the mauna and the Hawaiian community?
She emphasizes that this is not a one time conversation — this discussion needs to be ongoing and dynamic as situations and communities evolve. These principles also apply not only to the current situation surrounding the Thirty Meter Telescope and Mauna Kea, but also more generally to interactions with indigenous communities.
Amy Kalili and the meanings of ‘imi pono and pono ‘imi.
HEAD Bruno Rossi Prize, Kilonovae from Merging Neutron Stars (by Mike Zevin)
How do you turn iron into gold? In the final plenary lecture on Monday at #AAS235, Brian Metzger (Columbia University) and Dan Kasen (University of California, Berkeley) delved into kilonovae, the cosmic explosions responsible for synthesizing the heaviest elements in the universe. Metzger kicked things off by overviewing how heavy elements are created. When two neutron stars collide, they expel neutron-rich ejecta that bombard nuclei at a very high rate, forming large and unstable isotopes that then beta decay back to the valley of stability. This is known as r-process nucleosynthesis (see a visualization of this process here). This radioactive decay powers the kilonova explosion. GW170817, the binary neutron star merger detected by LIGO/Virgo and telescopes across the electromagnetic spectrum, beautifully exhibited this phenomena and produced thousands of Earth masses of r-process material in its cataclysmic collision.
Brian Metzger, a co-awardee of the HEAD Bruno Rossi Prize, describing the steps of a “well-behaved” neutron-star merger and kilonova.
Metzger pointed out that the emission from the kilonova provided important insights into the remnant that formed following the neutron star merger. Did the merger product immediately collapse into a black hole, or did it remain stable as a neutron star for a period of time? Metzger argued that we can rule out a prompt collapse for GW170817 because this scenario would not provide the necessary amount of ejecta that was observed. He also showed how we can rule out a long-lived neutron star, since this would lead to bluer emission than was observed. This points to the merger product of GW170817 likely proceeding through a “hypermassive” neutron star phase, supporting itself for a few hundred milliseconds before collapsing into a black hole. Interestingly, this tells us a great deal about the “equation of state” of neutron stars, which describes the pressure and density of neutron star matter in nature.
Kasen then took over, continuing the story of GW170817 and our understanding of kilonovae. Though Kasen “thought it would be 5 to 10 years before we were confronted with data”, the universe had other plans and provided a gold-plated kilonova on our doorstep only a short while after the Advanced LIGO/Virgo network began acquiring data. After recognizing the long list of authors that contributed to the GW170817 multi-messenger astronomy paper, Kasen noted that understanding kilonovae truly requires a multi-physics description, ranging from dynamics and mass ejection to neutrinos and nucleosynthesis to atomic physics to radioactive heating to radiative transport. Kilonovae provide a complex astrophysical environment and a heavy element factory; whereas about 1 billionth of our solar system is made of r-process material, kilonovae are the size of a solar system and are made up almost entirely of heavy r-process elements. Despite their complexity, theoretical predictions of kilonova light curves, color evolution, spectra, and temperature evolution all matched extremely well with the observations of GW170817. But despite the fact that GW170817 fit well with theoretical predictions, Kasen is confident that surprises await, and that we should have faith that nature is bound to provide something that will have astronomers scratching their heads.
Dan Kasen, a co-awardee of the HEAD Bruno Rossi Prize, schematically showing the blue and red components of a kilonova explosion.
