Editor’s Note: This week we’re at the 233rd AAS Meeting in Seattle, WA. 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 next week.

Plenary Talk: The Era of Surveys and the Fifth Paradigm of Science (by Mia de los Reyes)

“Science is changing,” says Alexander Szalay (Johns Hopkins University). Szalay began the first talk of the final day of #AAS233 by describing how the basic paradigm of science has shifted over time. He explained that science was for many centuries empirical, driven by observations of the natural world; as scientists began to explain these observations with underlying physics, it became predominantly theoretical. In recent decades, with the invention of computers, science became computational — and today, the growing dominance of “big data” is shifting science to a data-intensive paradigm.

Szalay then described the scientific landscape in this data-intensive world: data is everywhere, and it grows as fast as our computing power! This is primarily thanks to the rise of large surveys over the last 20 years. Szalay himself got involved with the data-driven side of astronomy through one such survey: the Sloan Digital Sky Survey (SDSS), an ambitious project that aimed to measure spectra of millions of objects across the whole sky (check out our coverage of the most recent SDSS press release here). In particular, Szalay helped build the Skyserver database at Johns Hopkins University. He describes Skyserver, the portal to access SDSS’s database, as a “prototype in 21st century data access” — it has become the world’s most used astronomy facility today, with over 1.2 billion web hits in the last twelve years!

The SDSS telescope at night [P. Gaulme]

On the other hand, Szalay then pointed out, SDSS has also revealed some of the major problems with big data. One such issue is lifecycles. Data and data services have finite lifetimes, as data standards, usage patterns, browsers, and software platforms all change. This opens up questions about the cost of preserving valuable data over the long term. Furthermore, we need to consider how to publish big datasets. The old publishing model of including data in printed publications clearly isn’t working, and we’re now moving to open data and open publishing (much in the same way that music publishing has largely transitioned from individual LP sales to distribution applications like Pandora and Spotify).

Szalay then asked, “How long can this proliferation of data go on?” Everyone wants more data, but “big data” also means more “dirty data” with more systematic errors. Szalay believes that we don’t simply need more data — we need to collect data that are more relevant. How do we do that? Perhaps this is the fifth paradigm of science, when algorithms make the decisions not only in data analysis, but also in data collection!  For example, machine-learning algorithms could use feedback from observed targets to choose their next targets. Finally, Szalay pointed out that to make the transition to this fifth paradigm, we need to change the way we train scientists: the next generation of scientists should have deep expertise not just in astronomy, but also in data science. So if you’re a young scientist, now might be a good time to start thinking about data!

Press Conference: Exoplanets and Life Beyond Earth (by Vatsal Panwar)

The last press conference on exoplanets was kicked off by AAS Press Officer Rick Feinberg, who remarked on the high share of exoplanet press conferences at this meeting.     

Direct imaging of Kappa And b [J. Carson]

Next up was a former Astrobiter! Benjamin Montet (University of Chicago) spoke about attempts to robustly detect transiting exoplanets in star clusters using the Kepler Space Telescope, the gift that keeps on giving. He noted that despite extensive searches for planets in the the data gathered by Kepler over ten years, there may still be some planets lurking in the data that we may have missed. The initial approach of extracting raw light curves for the Kepler dataset involved assigning a unique set of pixels to a star and performing conventional aperture photometry. However, this approach becomes less reliable if a star is in a crowded field — like in a star cluster. Finding planets in star clusters is useful as their ages can be pegged to the age of the cluster (which is relatively easy to determine). Properties of planets in clusters can hence help in understanding the long-term evolution of planetary systems. In this context Montet has been looking at the cluster NGC 6791, which was observed by Kepler for four years. By using Gaia astrometry of this region to determine accurate positions of stars in this cluster as observed by Kepler, his group has detected a number of planets in the cluster. Lack of short-period planets in this sample could be a hint of destruction of hot Jupiters due to tidal inspiral. This search also revealed 8 new eclipsing binaries and a few cataclysmic variable stars in the cluster. To conclude, Montet stressed that methods developed in this study will be relevant for looking at planets in star clusters observed by TESS.

Kate Su (University of Arizona) then talked about the studies of giant impact in the context of terrestrial planet formation. The usual pathway of terrestrial planet formation begins with the accumulation of pebbles, leading to the formation of planetesimals, which are the embryos of solid planet cores. However, this last step is also accompanied by the possibility of giant impacts, which might be a contributing factor to the diversity of compositions of the interiors of rocky exoplanets. A giant impact event of a large enough magnitude can trigger a steep brightening of the object in infrared wavelengths, which could be an observational signature of dust produced after collision. This is what’s believed to have happened in the star NGC 2457-ID8 in 2012 and again in 2014. The Spitzer Space Telescope observed a brightening of this disk in infrared back in 2012, which shows there was a spike in the amount of dust at that time. Dynamical and collisional simulations of this event have concluded that it would have happened around 0.43 AU to the star, and that the size of impactor must have been at least 100 km. Another impact in 2014 was observed by Spitzer in later stages of the survey, and this was even closer to the star with a 0.24 AU inferred separation.

Barnard’s star [Backyard Astronomer; P. Mortfield & S. Cancelli]

Plenary Talk: From Disks to Planets: Observing Planet Formation in Disks Around Young Stars (by Caitlin Doughty)

In this plenary talk, Catherine Espaillat (Boston University) discussed the state of the study of protoplanetary disks and what they tell us about planet formation. Planets form in protoplanetary disks around young stars, and the detected planets are diverse in size, composition, and their distances from host stars. However, both the planets and their formation processes are difficult to observe. Many astronomers pursue direct imaging of these protoplanetary disks, but disks can be easily outshined by bright host stars. This has fueled the need for exoplanetary scientists to cultivate a collection of indirect tracers of the presence of protoplanetary disks, especially in the early days of the field.

Espaillat began by presenting a brief history of the early study of protoplanetary disks, as well as what we currently know about these disks and planet formation. In the 1980s, when the spectral energy distributions of stars were studied, astronomers observed an excess in the anticipated infrared emission. Originally interpreted as possible activity from the chromosphere of the star, these were later explained by the presence of heated dust grains. By the 1990s, the Hubble Space Telescope had confirmed presence of dusty disks around stars. Magnificent edge-on images of disks were directly observed soon after. Later, the Spitzer Space Telescope and the Atacama Large Millimeter Array discovered gaps in several of these disks, and this culminated with a beautiful image of many small gaps HL Tauri.

Gaps in the disk of HL Tauri [ALMA]

Next, Espaillat discussed some of the so-called “footprints” of planet formation within protoplanetary disks. Since gaps within disks are believed to be created by planet formation, studies focus on the sizes and locations of gaps. Millimeter observations have shown a multitude of disks with gaps greater than 10 AU, but there is a diverse arrangement of disk structures, showing gaps of many sizes at many distances from the host. Some show bright spots or spirals, but they are typically quite symmetric. The small dust grain distribution in images reveals the flaring at the edges of disks and ripples in their surface structure, highlighting the complexity of their morphologies. Regarding planet formation, it is theorized that planets form most easily at snowlines within the disk, because >1-mm dust grains falling towards the host star may encounter the line and stop their fall, gradually coagulating onto one another to form planetesimals. However, ALMA observations have searched for gaps and planets at snowlines and have yet to turn up any evidence to confirm the theory.

Espaillat at #AAS233: Lots to learn from small grains too — including ripples and shadows on the surface of the disk pic.twitter.com/g0Bf3F1O3r

— astrobites (@astrobites) January 10, 2019

If there is relative consensus about indicators of planet formation, do we have any idea when they are forming? A logical consideration can provide an intuitive constraint: Planet formation has to occur before the dust disk has dissipated. It is observed that disk frequency around stars falls off with age, with few disks seen around stars older than 10 million years, and some stars even lose their disks at much younger ages. Dust evolution occurs in stars that are estimated to be only 1 million years old (quite young for a star), where indications of dust depletion are seen in the upper disk layers, one of the crucial first steps in planet formation. One interesting discovery is that HL Tauri is still being fueled by the molecular cloud it formed from; if this is a common occurrence, it could extend the potential disk-forming lifetime of stars. This remains an open question.

Espaillat ended the talk by emphasizing a few of the open questions about protoplanetary disks. As an example, how does gas accrete onto the star? Astronomers think that material from the disk “jumps” over the gap between the disk and the star and, tracing the magnetic field lines, is swept by the star’s gravity towards the poles. The amount of material affects the brightness of the accretion signal, meaning that we can use it to measure the accretion rate. It is expected that the rate should be affected by the size of the gap between the disk and the star, but scientists consistently find rates that are similar to one another. It is also seen that accretion rates can be variable with time, with system GM Auriga having shown an increase in measured accretion rate by a factor of four in a single week! The reason is unknown, but future observations are planned that will hopefully illuminate the cause. Future observations, once enough sensitivity is obtained, should also reveal the formation of moons around exoplanets! Espaillat ended by noting that next-generation telescopes like the Thirty Meter Telescope will help to resolve innermost disk structure, down to 1 AU, to help visualize what is happening there in these mysterious and dynamic objects.

Press Conference: Astronomers Have a Cow (by Mike Zevin)

In the 8th and final press conference of AAS 233, astronomers presented recent observations of everyone’s favorite farmyard animal in astronomy — AT2018cow, known by the astronomy community as simply “The Cow” (though “cow” was actually just a coincidental label assigned to this event). This powerful electromagnetic transient was discovered by the ATLAS telescope on 16 June 2018, residing in a star-forming galaxy approximately 200 million lightyears away.

Dan Perley (Liverpool John Moores University) kicked things off by summarizing the discovery — a new type of transient that was about 10 times more luminous than a typical supernova, or about 100 billion times more luminous than the Sun. The Cow was odd because of how “blue” it was, its speedy rise time (reaching its peak luminosity in only about 2 days), and its high-velocity ejecta (which reached speeds of about one tenth the speed of light). Telescopes from all over the world across all wavelengths observed this unique transient. In particular, Perley worked with the GROWTH network — a network of small telescopes around the world that were able to provide a nearly continuous view of the transient; they could observe continuously since there were always telescopes somewhere in the network that weren’t hindered by the pesky Sun. Its slow decay over time indicated that something was keeping it hot for many weeks after the explosion — a “central engine” which continually powered the ejecta. Two classes of models have been proposed for this supernova: the tidal disruption of a star by an intermediate-mass black hole or a special type of supernova involving a jet breakout. Perley commented that this explosion was similar to Fast Blue Optical Transients observed by prior surveys.

Location of AT2018cow [SDSS]

Amy Lien (NASA Goddard Space Flight Center & Univ. of Maryland Baltimore County) then continued the barnyard bash by highlighting one particular interpretation of the explosion: that it was caused by the tidal disruption of a white dwarf by a black hole. Since the source wasn’t centrally located in its host galaxy, it is unlikely that a supermassive black hole, the standard culprit of tidal disruption events, was responsible. Instead, it would have had to be disrupted by an intermediate-mass black hole of about 1 million solar masses residing in a globular cluster. Press release

After this, Anna Ho (Caltech) presented a perspective from longer wavelengths — observations in the sub-millimeter (i.e., wavelengths around the size of a grain of sand). The Cow was the brightest millimeter transient ever observed, brighter than any previously-observed supernova. It was first observed by the Submillimeter Array (SMA) in Hawaii, and was the first time a transient was observed to brighten at millimeter wavelengths. These observations, as well as follow-up millimeter observations by the Atacama Large Millimeter Array (ALMA) found that the Cow released a large amount of energy into a dense environment, and that it is a prototype for a whole new population of explosions that are prime targets for millimeter observatories.

Closing out the press conference, Raffaella Margutti (Northwestern University) presented a panchromatic view of the Cow, ranging from radio to optical to X-ray radiation. The key conclusions were that the Cow produced a luminous, persistent X-ray source that shined through a dense circumstellar environment rich in hydrogen and helium. Radio observations found a significant peak in the spectra from iron. Furthermore, the evolution of the radio light curve indicates that the explosion occurred in a dense interstellar environment, not something that would be found in a globular cluster. These pieces of evidence support the idea that the transient was caused by the explosion of a massive star and birth of a black hole rather than the tidal disruption event of a white dwarf by an intermediate-mass black hole. One of the most exciting features was found in the X-rays — a bump in high-energy X-rays known as a Compton bump. This is totally new for observations of supernovae, but has been observed in systems with accreting black holes, and thus suggests that the Cow had a newly-formed and accreting black hole at its center. All the light in the electromagnetic spectrum gave astronomers a different piece of same puzzle, and these pieces have come together to build a picture of this cow of a discovery. Press release

Plenary Talk: From Data to Dialogue: Confronting the Challenge of Climate Change (by Stephanie Hamilton)

Ten years. That is how long it took to put a man on the Moon. It is also how long we have to address climate change. And if we don’t? Well, the consequences are pretty dire. Dr. Heidi Roop of the University of Washington delivered the penultimate plenary talk of the meeting about climate change and what astronomers can do to help combat it.

Dr. Roop began her plenary by likening astronomers to climate scientists. We both think about unthinkable scales — what does 19,000 light years really mean? Or how about 800,000 years of climate data? We are humans who operate on human scales, and it is nearly impossible for us to wrap our heads around these scales as scientists, let alone for members of the general public. How can we possibly be changing an entire planet? Astronomers and climate scientists also both deal with the unknown. For climate scientists, the uncertainty is humans. Climate change is definitely happening, but the unknown is when we will gather ourselves and how we will mitigate and adapt to the effects of climate change.

The magic number plastered over climate-change coverage in the news is 1.5ºC. But why? There is a world of difference between overall global warming of 1ºC vs 2ºC over pre-Industrial Revolution levels. At 2ºC, two billion more people are exposed to rising water levels. Coral reefs will die off. 76 million more people will be affected by drought per month. And much, much more. We are on track to top 1.5ºC well before 2050 if we don’t act now — but mitigation by itself is not enough. How we feel future climate depends both on the actions we take now to mitigate the effects of climate change and how we prepare for what we’ve already set in motion. How do we adapt to a reality of more frequent and intense forest fires, which will also mean worsening hazardous smoke events? How do we adapt our coastal water treatment plants so that they will survive rising water levels? What trees should we plant today and where? The trees that thrive today almost certainly will not be the ones that thrive in a century.

Why do we care about 1.5 C of warning? #AAS233 pic.twitter.com/RfS7fjBd8o

— Jacob White (@Jacob_White26) January 10, 2019

So what can we as astronomers do? All of these questions seem like insurmountable problems. After all, “solve climate change” is a pretty tall ask, especially for any one person. So how can we start to effect change? One of the most important things is to simply have the conversation and talk about climate change. Only 36% of American adults have that conversation at all. That number is likely higher among scientists, but surveys and polls have shown that simply talking about climate change is the third most influential factor on Americans’ opinions on the subject. Climate scientists have started speaking out in public fora. As astronomers, we have a degree of trust and credibility that even climate scientists don’t have, so we need to talk about the problem.

We also need to make climate change a local problem. As Dr. Roop pointed out, most people on the east coast probably don’t care about what will happen in Seattle. They care about what will happen in their own communities, so we need to make the effects of climate change clearly local and personal. Polls indicate that most people want action on climate change and at all levels of government — so talk to your elected officials about climate-friendly policies and hold them accountable.

One of Dr. Roop’s slides

How do we talk about climate change in a way that people will listen to? Dr. Roop recommended sticking to five simple and sticky themes: it’s real, it’s us, experts agree, it’s bad, and (importantly) there’s hope. Good messages must have emotional appeal and make the facts specific and personal to whoever you are talking to. In the era of the internet and free information, though, misinformation is a serious concern and sometimes also feels like an insurmountable problem. But people do not like being lied to or deceived, so a way to combat misinformation is to teach people the manipulative tactics used to spread it so they will be more on-guard. Finally, simply touting prospects of doom and gloom is not a good way to inspire people to act, so find local stories of hope and action — and spread them. The facts of climate change will follow the stories.

So how do we solve climate change? We teach. We talk. We listen. We learn. And most importantly, we act.

Plenary Talk: Lancelot M. Berkeley Prize: The XENON Project: at the Forefront of Dark Matter Direct Detection (by Nora Shipp)

Elena Aprile (Columbia University) gave the final plenary of the meeting. She presented the Lancelot M. Berkeley Prize Lecture on the search for dark matter with the XENON Project. The XENON Project is an experiment for the direct detection of Weakly Interacting Massive Particles (WIMPs). Aprile reminded us that the WIMP is only one of many classes of dark matter particle, but it is one that fits very nicely into physical theories. XENON is one of several experiments that has pushed down the limits on WIMP models in recent years, limiting the possible range of masses and cross-sections, and narrowing down the range of possible dark-matter particles.

The XENON experiment underground [XENON collaboration]

The background limits on the WIMP dark matter cross section from the XENON1T experiment so far. [Aprile et al. 2017]

The latest version of the XENON experiment is XENON1T, with 1.3 tons of cryogenically-cooled liquid xenon, and a smaller background than any previous experiment. It has placed the strongest limits to date on the WIMP scattering cross-section (for spin-independent interactions and a WIMP mass above 6 GeV). This is not the limit of the XENON project, however. Aprile presented plans for XENONnT, an even more powerful detector, with 8.4 tons of liquid xenon, which should improve the sensitivity to dark matter models by another order of magnitude in the coming years.

Editor’s Note: This week we’re at the 233rd AAS Meeting in Seattle, WA. 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 next week.

Plenary Talk: The Energetic Universe in Focus: Twenty Years of Science with the Chandra X-ray Observatory (by Mia de los Reyes)

The Chandra X-ray Observatory is now almost 20 years old! Ryan Hickox from Dartmouth College started off the third day of #AAS233 by reviewing some of the remarkable discoveries that Chandra has made in the last two decades.

First, Hickox reminded everyone why exactly X-rays are so useful: they probe the bulk of the baryonic matter in the universe, especially in extreme environments. He also discussed the basic capabilities and structure of Chandra before turning to some of the major science questions that Chandra has helped answer.

Part 1: The lives and deaths of stars

Chandra has been used to study star-forming regions like Orion, monitoring how young stars produce intense X-ray flares.

Here’s an outline of Hickox’s talk. He’s now discussing the role of @chandraxray in studying star forming regions. He shows an example with a deep Chandra image of Orion. #AAS233 pic.twitter.com/FPJ9HV8OWQ

— Peter Edmonds (@PeterDEdmonds) January 9, 2019

Hickox then turned to the deaths of stars, highlighting beautiful X-ray observations of the supernova remnant Cas A. Chandra has observed the X-ray spectrum of Cas A and mapped out the spatial locations of different elements in the remnant, helping astronomers understand the explosion mechanism and how different elements were produced in the supernova. Chandra has even directly observed the neutron star at the center of the Cas A remnant!

Part 2: The growth and evolution of galaxies and black holes

“Chandra’s done lots of other work trying to understand black holes,” Hickox noted. For example, Chandra obtained a spectrum of the black hole binary GRO J1655; the absorption lines in the spectrum were strongly blueshifted, suggesting that large amounts of material are outflowing from the binary system. Such a large wind of material may be magnetically driven.

Chandra image of Centaurus A, a galaxy hosting a gargantuan jet. [NASA/CXC/U.Birmingham/M.Burke et al.]

Hickox’s own research aims to understand these active galactic nuclei (AGN). In particular, what drives the growth of supermassive black holes over cosmic time? What’s the difference between AGN and other passive galaxies? X-ray surveys are uniquely suited to study these questions, because they can identify weak or obscured AGN that are undetectable in other wavelengths. Indeed, X-ray surveys with Chandra have found AGN in all types of galaxies; these data have shown that although black holes grow along with host galaxies over cosmic time, they “flicker” on short (less than million-year) timescales! These observations have opened more exciting questions about how exactly these black holes grow over time.

Part 3: Large-scale structures and their cosmic history

On even larger scales, Chandra has been used to probe the most massive structures in the universe. Chandra observations of the Virgo cluster have identified huge bubbles of hot gas around the galaxy at the center of the cluster, showing that the central galaxy is an AGN injecting energy fast enough to keep gas from cooling and forming stars. This impressive finding demonstrates that black holes regulate baryons on large scales in the universe!

Chandra observations have also been used to directly probe dark matter! The Bullet Cluster is one of the most famous examples of the direct observation of dark matter. The hot gas in the cluster, observable in X-rays, comprises most of the baryonic mass in the cluster. However, this gas is spatially offset from the total mass observed with gravitational lensing, suggesting that there is another source of matter — dark matter — in the cluster. Through this and other measurements, Chandra has helped obtain key constraints on cosmological parameters.

These won’t be the last of Chandra’s discoveries. As Hickox says, “Chandra is good to go!” The Chandra team expects at least ten more years of observations! They’re also starting to think about what comes next. Hickox says that deeper X-ray observations with greater instrument sensitivity and angular resolution will be needed to probe signatures of the first black holes, and we’re looking forward to see what future X-ray missions may bring.

Press Conference: Things That Go Bump in the Night Sky (by Susanna Kohler)

This morning’s conference was presided over by Astrobites’ own Kerry Hensley, in her capacity as the AAS Media Fellow. Welcoming a packed room, Kerry kicked off a session full of exciting results that stand to significantly advance our understanding of — for lack of a better word — weird astronomical phenomena.

The CHIME telescope incorporates four 100-meter long U-shaped cylinders of metal mesh. [CHIME]

Why is this a big deal? Of the ~60 FRBs detected so far, only one had previously been known to repeat. This source led both to questions — is this repeating burst rare or unusual? If not, why don’t the other bursts repeat? — and to answers: the repeating burst allowed us to finally hunt down an FRB source location. CHIME’s discovery of a second repeating burst suggests that repeating FRBs perhaps aren’t so rare after all, and it provides us with further opportunity to look for the origin of these weird signals and, hopefully, figure out what they are! Press release

Artist’s illustration of a magnetar, a rotating neutron star with incredibly powerful magnetic fields. [NASA/CXC/M.Weiss]

Rounding out the session, Erin Kara (University of Maryland) presented exciting new results in the world of X-ray binaries, or black holes accreting matter from a binary stellar companion. One of the big mysteries of X-ray binaries is what causes their emission to change over time: sometimes the X-ray emission is dominated by light from the disk of accreting material, but sometimes it’s dominated by light from the hot cloud of gas that lies above the disk, known as the corona. New observations from NASA’s Neutron star Interior Composition Explorer (NICER), an X-ray detector mounted on the International Space Station, have shown one X-ray binary’s corona contracting over the span of several weeks, shrinking from hundreds of miles to just ~10 miles in vertical extent. This observed change in structure may provide insight into how material funnels onto stellar-mass black holes and releases energy in the process. Press release

Plenary Talk: The Climates of Other Worlds: Exoplanet Climatology as a Pathway to Accurate Assessments of Planetary Habitability (by Vatsal Panwar)

Aomawa Shields (University of California Irvine) gave the next plenary talk of the day on the ongoing hunt for the holy grail of exoplanet science — an Earth-like habitable planet. Shields started off by referring to the first image of Earth taken by Apollo 17 (The Blue Marble) and recalling that until about two decades ago, before the discovery of first exoplanets, we believed that Earth was possibly the only habitable planet. With 3,885 confirmed exoplanet detections to date, we have come a long way since then — largely due to the Kepler Space Telescope, which detected transiting exoplanets for the last 9 years.

With the baton now passed to the Transiting Exoplanet Survey Satellite (TESS) — the first all-sky survey of its kind in space — we will soon be discovering many more Earth-analog planets (in terms of size and mass), which will be quite interesting to follow up for characterisation. In particular, systems similar to TRAPPIST-1 around M dwarfs in the solar neighbourhood will be the most ideal targets for atmospheric characterisation by infrared instruments on the upcoming James Webb Space Telescope (JWST) and Extremely Large Telescopes, and next generation concept missions like LUVOIR, HabEx, and Origins Space Telescope.

Shields emphasised that some of these newly detected planetary systems could really push the definitions of a habitable planet. Prioritising the ones for follow-up studies in this context would require a good understanding of a planet’s climate and the observable biosignatures associated with it.

#AAS233 plenary by Aomawa Shields on habitable planet climates around other stars. There are a bewildering number of factors that go into “habitable!” pic.twitter.com/chL5re0B5k

— Ward Howard (@WardHoward4Him) January 9, 2019

From our understanding of life as we know on Earth, some of the essential ingredients to sustain biological metabolism are liquid water; availability of bioessential elements like carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulphur; and a source of energy. The current search of habitable worlds primarily hinges on detection of liquid water. However, the dense web of dependencies between the factors governing a planet’s ability to sustain liquid water on its surface suggests how difficult it is to theoretically model a planet’s habitability. Shields has been developing a hierarchy of planetary climate models centred around the conventional general circulation models that take into account physical aspects governing a planet’s climate, like radiative–convective heat redistribution, overall energy balance, and planetary orbit and rotation. There are several other factors like the obliquity of a planet, spectral type of its host star, and variations in stellar irradiation levels, surface pressure, and synchronous rotation that control the climate and the habitability of a terrestrial planet.

Artist’s impression of Earth in a “snowball state”. [NASA Astrobiology]

For instance the wavelength band in which water ice is most reflective (blue end of the optical spectrum) overlaps with the band in which a G-type star like the Sun is most bright. In comparison, the ice albedo is much less in bands where M dwarfs are most bright (redder end of the spectrum), which means that it is much harder for a terrestrial planet around an M-dwarf star to go into a snowball state due to ice albedo feedback. However other effects like cloud formation, extent of atmospheric circulation, and salinity of surface ice are also responsible for deciding how easily a planet can get into a snowball state. In case of a multiple-planet system, the dynamical evolution of the system also affects a planet’s climate over geological timescales.

Shields and her group are working on tackling the subtle climatic and geological phenomena that ultimately decide a planet’s habitability. She concludes that going from “an artist’s impression to an actual photograph” of a terrestrial exoplanet and being able to assess its habitability correctly would need careful co-development of both observations and theory that comprehensively consider all of these factors.

Press Conference: Black Holes and Galaxies Near & Far (by Caitlin Doughty)

To start off the press conference, Xiaohui Fan (University of Arizona), announced the discovery of a quasar at redshift z=6.51, corresponding to a distance of 12.8 billion light years away, seemingly with an inherent brightness of 600 trillion solar luminosities, which would make it the brightest known quasar. Noting some apparent contaminants in the quasar’s spectrum and a slight stretching in the images, Fan and collaborators obtained deep HST images of the system and were able to observe what was really going on: the quasar is in fact being gravitationally lensed by a foreground galaxy located at z=0.6. It’s split into three images by the complex arrangement of matter in the foreground lens, and it’s magnified by a factor of 50. This also indicates that the quasar’s true luminosity is on the order of 12 trillion solar luminosities, relatively faint. Spectra from the Very Large Telescope will let Fan and collaborators study the intervening absorption and learn about late-stage cosmic reionization, while upcoming observations by the Atacama Large Millimeter Array (ALMA) will allow study of the region within 150 light years of the black hole, i.e., within its gravitational influence. Future work will also hopefully address whether there is an unknown population of lensed quasars. Press release

I’m at the upcoming #AAS233 press briefing on black holes which includes two separate @chandraxray results. One of them is led by Amalya Johnson (2nd from right) from Columbia & the other by DJ Pasham (2nd from left) from MIT pic.twitter.com/EF4VVw0Wsa

— Peter Edmonds (@PeterDEdmonds) January 9, 2019

Next, Dheeraj Pasham (MIT Kavli Institute for Astrophysics and Space Research) reported study of an astrophysical transient called a tidal disruption flare, which led to the calculation of the spin of a black hole. A tidal disruption flare occurs when a star ventures too close to a black hole and is gradually shredded, the raw material settling into an accretion disk around the black hole. The infalling material heats up, reaching millions of degrees Celsius and emitting abundant X-rays as a result. The flare that spurred this announcement was observed in the All-Sky Automated Survey for Supernovae (ASAS-SN), and it sprang from the center of a galaxy roughly 290 million miles away from Earth. Careful analysis of the light curve of the X-ray signal showed a flicker in the brightness that occurred every 130 seconds. This flicker is related to the spin rate of a clump of material orbiting the black hole, and thus to the black hole spin rate. Pasham found that the material is orbiting at about 50% the speed of light, about 334 million miles an hour. This high rotation speed indicates that the black hole probably grew by pulling material off an accretion disk rather than by merging with other black holes. Further study of these tidal disruption flares may allow study of how black holes grew as the universe aged. Press release

The radio galaxy Cygnus A showing locations of jets, hotspots, and the hole surrounding hotspot E. Credit: X-ray: NASA/CXC/Columbia Univ./A. Johnson et al.; Optical: NASA/STScI

The third story was reported by Amalya Johnson (Columbia University), and gives evidence of a jet “ricocheting” off of a hotspot in the radio galaxy Cygnus A. Based on a Chandra X-ray observatory study of Cygnus A, located 600 million light years from Earth. The galaxy hosts an Active Galactic Nucleus (AGN) and jets creating lobes on the eastern and western fronts of the galaxy that glow brightly in the radio. The ricocheting effect was discovered upon noticing that so-called hotspot E in the galaxy, one of several small, radio-bright clumps created where the jet material encounters the intergalactic medium, was surrounded by an apparent lack of X-ray emission. The region lacking X-ray emission is a hole, deeper than it is wide, which indicates that the jet material is ricocheting off the material in hotspot E and being redirected towards another region, called hotspot D. There is also some indication that a similar ricocheting effect may be happening between the hotspots on the western side of the galaxy, between hotspots B and A. Press release

For the last story, Erik Rosolowsky (University of Alberta) reported on some preliminary from the Physics at High Angular Resolution in Nearby Galaxies with ALMA (PHANGS-ALMA). This current survey, with nearly 90% of observations already complete, is designed to observe 74 nearby galaxies and 100,000 molecular clouds (MCs) with the ultimate goal of discovering whether MCs are more efficient at forming stars in low-mass galaxies or in high-mass galaxies. The survey covers a wide range of galaxy masses and star formation rates to improve the robustness of their results. After mapping emission from the carbon monoxide molecule and counting the youngest stars in close proximity to the clouds, Rosolowsky has preliminary results from 12 of the eventual 74-galaxy sample that suggest that low-mass galaxies may actually be more efficient at transforming molecular gas into stars. The end goal of this work is to determine the effects on the MCs by the conditions in the host galaxy. Press release

Plenary Talk: Annie Jump Cannon Award: Tracing the Astrochemical Origins of Familiar and Exotic Planets (by Kerry Hensley)

It’s a really exciting era to study planets and planet formation! Dr. Ilse Cleeves (University of Virginia), winner of this year’s Annie Jump Cannon Award for “groundbreaking work on planet formation and protoplanetary disks,” explained our current understanding of the chemistry of protoplanetary disks, the questions left unanswered, and what we can hope to learn in the future.

We’ve reached the point where we’re able study not only the atmospheres of distant stars, but also the atmospheres of the planets that orbit them. Despite our ability to detect whiffs of gases in far-off atmospheres, there’s still plenty we don’t know about our own planet: Where did Earth get its water? Why does it have less carbon and nitrogen than we expect? What’s the core made of? These are just a few of the lingering questions we have about the planet we know the most about!

Even if we could explain every facet of Earth’s formation, though, we would still be far from explaining the wide diversity of planetary and solar system bodies — from Jupiter with its nearly solar composition (but curiously high carbon and low oxygen abundance) to comets, the “icy time capsules” of the early solar system. And when we consider all the truly wild forms that exoplanets can take (lava worlds and diamond planets, I’m looking at you), we have to ask the question — where does all this diversity come from? The answer, of course, is the chemistry happening in protoplanetary disks!

The presence of snow lines has a huge effect on the chemical environment from which planets form.

Thanks to changing radiation levels, dust grain sizes, and gas temperature, it’s possible for planets formed from the same stellar nebula to have vastly different core and envelope (aka atmosphere) compositions. For example, as we move farther away from the star, the gas temperature drops and chemical species like water, carbon dioxide, and carbon monoxide gradually freeze out as solids. This transition changes the ratio of carbon to oxygen in both the gaseous and solid material, which drives different chemistry; high C/O ratios tend to yield lots of hydrocarbons, whereas abundant oxygen leads to lots of CO. Plus, at a more fundamental level, the gradual freezing out of molecules as you move away from the star changes the material available to be accreted onto a planet: If CO2 is a solid where the planet is forming, there won’t be any CO2 in its atmosphere.

We’ve been able to make huge advances in studying disk composition and structure with observatories like Herschel and the Atacama Large Millimeter/submillimeter Array (ALMA). In order to understand fully what’s going on in protoplanetary disks, we need to combine observations with both modeling and laboratory studies. Plus, protoplanetary disk astrophysicists — like so many members of our community — are eagerly awaiting the launch of the James Webb Space Telescope (JWST), which should greatly enhance our understanding of disk chemistry and help us learn how planets form. Keep your fingers crossed for successful testing and a smooth launch!

Cleeves concludes with optimism for the future: continued improvements in observations and models are sure to keep advancing our understanding of the environments in which planets form. @NASAWebb can’t get here soon enough! #AAS233 pic.twitter.com/0HphArUe7d

— astrobites (@astrobites) January 10, 2019

Plenary Talk: Henry Norris Russell Lecture: The Limits of Cosmology (by Stephanie Hamilton)

There is a lot we don’t know about our universe. In fact, we call 96% of it “dark” because we can’t see or measure it directly with any of the methods we’ve developed thus far, all of which rely on light. Worse, we’re starting to reach the limits of what our current methods can do in terms of probing the nature of dark matter and dark energy. Dr. Joseph Silk, professor at Johns Hopkins and the 2019 Henry Norris Russell lecturer, recapped the status of both fields in the final plenary of the day and suggested some possible next steps (spoiler: it may involve telescopes on the Moon!)

Dr. Silk’s hand-drawn, colorful plots received a laugh as he simultaneously advised researchers not to forget the pretty colors.

Dr. Silk kicked off his plenary talk with some advice for younger researchers. He noted that sometimes success happens by being in the right place at the right time, so take advantage of opportunities that arise! He also advised that intuition isn’t always enough to “come to grips with the universe” — often, the data reveal completely unexpected results. Dr. Silk’s next piece of advice was to make sure you do at least one analytical project, but don’t forget about the data or the pretty pictures. Finally, he encouraged young researchers to choose an interdisciplinary field where there is a gap to be bridged.

Dark matter is a mysterious substance whose existence we know of only through its gravitational effects. Attempts to explain it away with theory have been unsuccessful, and astronomers have now accepted that it really must exist. Leading theories predict that it is some type of weakly interacting massive particle (WIMP), forcing direct detection experiments underground so as to escape the bombardment of cosmic radiation that would otherwise overwhelm detectors with noise. Unfortunately, nothing has been discovered yet, and our experiments keep getting bigger and bigger. We are rapidly approaching the dreaded “neutrino floor,” below which even neutrinos (which would interact with one atom on average passing through a light-year of lead) become a significant source of noise.

Not all is lost, though. When dark matter particles collide, astronomers think the collision would result in a measurable gamma-ray signature. Further, collisions of protons at the LHC could produce dark-matter particles that would appear in analyses as missing energy. In a different proposal altogether, a prevalence of sub-Earth-mass black holes remains a viable, albeit unlikely, explanation of dark matter that doesn’t require any new physics to explain. Scientists are already studying these phenomena, though none have yet explained dark matter.

Dr. Silk then shifted gears to dark energy. So far, experiments suggest that dark energy is explained by a cosmological constant, or a constant vacuum energy density. But we have not converged upon a single model, and there are still open questions. Measured values of the universe’s expansion, H0, differ between early- and late-time experiments, suggesting a possible need for new physics. Further, we do not yet have the sensitivity to distinguish between various models of inflation. Precision cosmology using either the cosmic microwave background (CMB) or galaxies is limited simply by the number of features we can measure. Thus, we need a method that gives us a larger number of objects to measure.

The solution? The Moon! Specifically, Dr. Silk proposed studying the gas clouds in the universe’s dark ages via 21-cm astronomy (enabled by the hyperfine atomic transition of hydrogen). The problem here is that not only will features so far away (redshift z~50) be incredibly faint, but the redshifted 21cm signal falls into the noisy radio bands of Earth. The far side of the Moon happens to be the most radio-silent place in the Solar System — perhaps the next step for understanding our early universe is the construction of a radio telescope on the Moon!

Interesting proposal from Joseph Silk to establish radio telescope arrays in the far side of the Moon – most radio-quiet location in the solar system!#aas233 pic.twitter.com/dsfRBP3tPp

— Alice Monet (@alicemonet) January 10, 2019

Special Session: Implementing the Next Decadal Survey: Status Report of Astro2020 from the Committee on Astronomy and Astrophysics at the National Academy of Sciences (by Susanna Kohler)

What’s planned for the next decade of astronomy? We went to the Astro 2020 Decadal Survey Town Hall to find out.

What’s planned for the next decade of astronomy? We’re at the Astro 2020 Decadal Survey Town Hall to find out. #aas233 pic.twitter.com/NE1GITi0ox

— astrobites (@astrobites) January 10, 2019

The Decadal Survey is a process implemented in astronomy every ten years, during which the astronomy community determines — hopefully by consensus — what to prioritize for government investment over the next ten years. These priorities can include missions large and small, facilities, and programs.

In the town hall tonight, the co-chairs of the Decadal, Fiona Harrison and Rob Kennicutt, outlined the process ahead. Though it’d be awesome if we could simply fund all our favorite missions and projects, the reality of the Decadal process is much more complex than this, and it requires careful research and difficult decisions.

The first step is for members of the astronomy community to submit what are known as “white papers” — brief summaries of what’s important in the scientific future of a specific subfield, discussions of the state of the profession, etc. These white papers can be submitted by a lone individual with a great idea, or by groups of scientists who all converge on support for a single project or goal.

Fiona Harrison and Rob Kennicut, the chairs of the Astro Decadal process, describe the next step: the astronomy community can submit short science white papers to the survey committee. #aas233 pic.twitter.com/4FefhO4Xgf

— astrobites (@astrobites) January 10, 2019

Harrison and Kennicutt repeatedly emphasized the importance of community involvement via white papers, attending town halls and public discussions, etc. — the goal is not for the Decadal survey committee of 18 people to make decisions in a vacuum about what astronomy should be pursued in the next decade, but rather for the whole community to participate in this process. In particular, early-career scientists are encouraged to get involved: Harrison commended grad-student journal clubs, for instance, that meet to plan white-paper submissions.

To learn more about the Decadal, and to submit white papers or nominate committee members, you can go here. Keep an eye out for the white-paper deadline on 19 February 2019, and the deadline for nominations to the survey committee, 22 January 2019. And keep an ear to the ground as we continue to develop our priorities as a community for the next ten years of astronomy!

Editor’s Note: This week we’re at the 233rd AAS Meeting in Seattle, WA. 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 next week.

Plenary Talk: Beatrice M. Tinsley Prize: One Large Galaxy with One Small Telescope (by Caitlin Doughty)

In the first plenary talk of Tuesday, Julianne Dalcanton gave a talk describing the research that garnered her the Beatrice M. Tinsley Prize, which is awarded for an outstanding research contribution to astronomy “of an exceptionally innovative character”. In this talk, Dalcanton described the research topics through the trajectory of her career from her graduate studies of low surface brightness (LSB) galaxies to her current work on the Panchromatic Hubble Andromeda Treasury (PHAT). On the advice of fellow astronomer Sarah Tuttle, she promised “some story, a few adventures, and a little wow”.

Julianne Dalcanton shares some story and a little WOW about galaxies at #aas233 pic.twitter.com/jeNFLkX5km

— Dr Heidi B. Hammel (@hbhammel) January 8, 2019

After transitioning to a post-doctoral researcher position, her interest in LSB galaxies transformed into curiosity about their dust structures. One successful Hubble Space Telescope (HST) proposal later she was left with many images of LSB galaxies, analysis of which revealed a discouraging lack of dust. However, it was noted that there were an astonishing number of fully resolved stars visible in the HST images. Dalcanton elected to make lemonade from these dustless lemons by using the stars to create Color Magnitude Diagrams (CMDs), which encode many properties of stellar populations, including information about the ages of the stars. By modeling single stellar populations (i.e. groups of stars with the same age and metallicity) and making CMDs of the model populations, Dalcanton and her collaborators were able to find ways to combine the different populations into one composite CMD that matched the ones observed in their target galaxies. This mean that they were able to recreate the star formation histories of these galaxies, learning about the timing of their star formation episodes and even how many episodes there were.

Dalcanton then embarked on a quest to study galaxies in the Milky Way’s own backyard using the Advanced Camera for Science (ACS) on HST as part of the ACS Nearby Galaxy Survey Treasury (ANGST). The goal was to generate a set of observations of Local Volume galaxies in multiple colors that were relatively uniform, since earlier observations of the same galaxies had been taken by astronomers working on very different projects with different goals, meaning that it was more difficult to make comparisons between those observations. ANGST observed 69 galaxies before the power supply on the ACS instrument failed, leaving Dalcanton and her collaborators short of their original goal.

A figure showing @dalcantonJD discovering that the nearby universe is the best, most interesting part of the universe ❤️ #AAS233 pic.twitter.com/RrMw8fOoob

— Johnny Greco (@johnnypgreco) January 8, 2019

With this setback, Dalcanton resolved to start observing much closer galaxies. Doing so allows astronomers to see more, fainter stars, and it enables detailed study of high surface density regions (for example, in the disks spiral galaxies) that would be impossible for a more distant target due to resolution limitations. However, having not quite let go of her original wish to assemble a large survey with HST, she proposed the PHAT program. 12,834 images, 414 positions, and over 39 months later, Dalcanton’s team has produced photometry of 117 million stars in Andromeda and multi-wavelength images in ultraviolet, optical, and near-infrared filters. In tandem with the benefits of observing nearby Andromeda, the relative abundance of information about its stars — such as their distance and their physical environment — let Dalcanton and collaborators remove some of the degeneracies inherent in CMDs and create HR diagrams in their place. From these diagrams, they can even infer what an image would look like when taken with a filter that wasn’t originally included in PHAT!

Throughout her talk, Dalcanton peppered her slides with acknowledgements of the mentors, collaborators, and students who have been instrumental in the success of these many projects, thanking them for their dedication to the work. Judging by the audience response to her talk, there is little doubt that they are all thankful for her as well!

Press Conference: Mysteries of Planet Formation (by Stephanie Hamilton)

The first press conference of the day also marked the third exoplanet-related press conference (out of three total) of the meeting. AAS Press Officer Rick Feinberg noted that this meeting received the highest number of exoplanet paper submissions in the meeting’s history.

Carol Grady (Eureka Scientific) kicked off the session by announcing the observed erosion of AU Microscopii’s protoplanetary disk. Observations from the Hubble Space Telescope revealed features in the disk that move visibly outward on the scale of 8–9 months. Astronomers do not know how the blobs are being launched through the system. Grady noted that the size of the features is commensurate with coronal mass ejections in our own solar system, but astronomers need additional data to confirm or deny this hypothesis. Press release

Plot of exoplanet mass versus orbital semimajor axis. The “desert,” a region empty of planets, is starkly evident.

The discovery of hot Jupiters (giant planets extremely close to their stars) was a surprise to astronomers. They have since been developing models of how such planets could come to exist. Elizabeth Bailey (CalTech) next announced new results that support the in-situ formation model. Plotting discovered exoplanets’ masses versus the semimajor axis of their orbits reveals a sharp cutoff called “the desert” (see figure to the right), named such because it is a region devoid of planets. Bailey’s models of the protoplanetary disk, which include accretion that supply the in-situ hot Jupiters with material, accurately reproduce this cutoff. While the model remains agnostic toward how the planet cores arrived at the close-in orbits, meaning migration may still play a role, the results show that hot Jupiters may indeed form in-place. This is contrary to the long-standing belief of the past two decades.

Next up, Aparna Bhattacharya (NASA Goddard Space Flight Center) described efforts to discover “cool” planets (i.e., those beyond the snow line) through microlensing using Hubble and adaptive optics on the Keck Telescope. By observing the microlensed system OGLE-2012-BLG-0950 over six years, during which time the system has moved and the source is no longer lensed, Bhattacharya and colleagues discovered the presence of a 39-Earth-mass cool planet. Cool planets are generally difficult to find with other exoplanet discovery methods due to their greater distances from their stars. WFIRST will use this method to discover and measure the masses of hundreds of exoplanets. Press release

Comparison of Saturn and Neptune to an artist’s conception of planet OGLE-2012-BLG-0950Lb. [NASA/JPL/Goddard/F. Reddy/C. Ranc]

Did the 39-Earth-mass exoplanet discovery catch your attention? David Bennett (NASA Goddard) rounded out the conference continuing discussion of possible formation mechanisms for these types of planets. Core accretion is the leading theory, but is it right? 39 Earth-masses sits in between Jupiter-like and Neptune-like planets. Core accretion struggles to explain these middling-mass planets because either runaway accretion was triggered (leading to Jupiter-like planets), or it wasn’t (leading to Neptune-like planets). 3-D hydrodynamical simulations of planetary formation suggest that perhaps runaway accretion is not necessary, but many scientists are not convinced. WFIRST will find many more of these middling-mass planets and help complete the full exoplanet picture. Press release

Plenary Talk: AAS Task Force on Diversity and Inclusion in Astronomy Graduate Education (by Nora Shipp)

In the second plenary of the day, the AAS Graduate Diversity and Inclusion task force addressed the critical issues of equity and inclusion in graduate education. They recommended steps that individuals, departments, and the AAS can take to improve graduate recruitment, admissions, and mentoring. These recommendations are published in a 70 page report, which can be found here.

First, the working group on graduate admissions stated their three primary goals:

1. The demographics of admitted students should match those of qualified applicants.
2. Admissions committees should broaden their definitions of excellence and merit.
3. The process of applying to grad school should be transparent.

The working group made several suggestions, including forming relationships with institutions that support students from under-represented groups such as Historically Black Colleges and Universities (HBCUs), Hispanic Serving Institutions (HSI), Tribal Colleges, and bridge programs. It also recommended using a holistic, evidence-based approach to graduate applications by rejecting the use of standardized tests and using clear rubrics. Additionally, it suggested that departments work together with their universities to address issues related to application fees, funding, and mandatory application materials.

Next, the working group on retention discussed how we can work to make graduate programs supportive environments for students from under-represented groups. It argued that we must end harassment and bullying in and around astronomy departments; provide an accessible environment, including, but not limited to, full ADA compliance; provide a healthy, welcoming, family-friendly environment; provide effective mentoring and networking; and adopt teaching and learning practices that support all students. It encouraged departments to ensure that all students have more than one close mentor, that all advisors receive mentoring training, and that students are assigned near-peer mentors and mentors with shared minoritized identities. Implementing these policies, the working group emphasized, will not be easy, and it will require engaging in genuine and often uncomfortable conversations with all members of the community and continually reassessing the effectiveness of programs put in place.

The final working group discussed the collection of data and the assessment of progress. It encouraged departments to participate in national demographic and climate surveys distributed by the AAS and AIP, and to request site visits, such as the new Climate Site Visit Program offered by the AAS. It also recommended that the AAS establish a platform where departments can share their progress to recognize departments making important changes and to incentivize others to follow their lead. Individuals, departments, and the AAS must all work together to hold each other responsible for making these essential changes that will allow students of all identities to feel welcome in our field.

Special Session: NASA Decadal Preparations: Large Mission Concept Studies (by Susanna Kohler)

What’s the next big space mission in NASA’s future? We don’t know yet — nor do any of the four teams developing proposed flagship mission concepts for the 2020 NASA Decadal Survey for Astrophysics. Due to limited funding, these missions will not all come to fruition. Instead, though all four teams will work for years to develop detailed plans, the scientific community will ultimately recommend just one of the four as the top priority for pursuit in the coming decade.

Though this seems like a potentially sad story, the truth is it’s a win for astronomy in any outcome. All four missions are remarkably broad and will enable unprecedented exploration of our universe — both to answer current questions and to conduct science we’ve not yet even imagined.

Four proposed space missions for the next decade would probe fundamental astronomical questions, like where we come from and whether there are habitable worlds elsewhere. [ESA, NASA, and L. Calcada (ESO for STScI)]

The Lynx X-ray observatory would be a transformative X-ray telescope with a hundred-fold increase in sensitivity, 16 times the field of view, 800 times the survey speed, and 10–20 times the spectral resolution of our current X-ray heavy-hitter, the Chandra space telescope. Lynx would be able to probe a broad range of science topics, including the dawn of black holes, the drivers of galaxy evolution, and the energetic side of stellar evolution.

The Origins Space Telescope is an infrared telescope that would be a factor of 1,000 more sensitive than previous infrared space telescopes — an advancement achieved just by cooling the telescope. Since half of the light emitted by stars, planets, and galaxies over the lifetime of the universe emerges in the infrared, Origins would open a window onto a broad range of fundamental origins questions from our cosmic history — like “How does the universe work?”, “How did we get here?”, and “Are we alone?”

The Large UV/Optical/Infrared Surveyor (LUVOIR) would be a powerful multi-purpose observatory. The LUVOIR team isn’t kidding with its name: the proposed 8-meter or 15-meter primary mirror for this mission definitely qualifies as “large” for a space telescope. As with the other missions, LUVOIR has a broad range of science goals — such as exploring the epoch of reionization, learning about galaxy formation and evolution, and searching for biosignatures in exoplanet atmospheres.

.@astronomeara giving a great #LUVOIR talk now. Also points out that all four concept teams dedicate years of our too-short lives designing missions that may never fly. We’re all feel each other’s pain and we’ll all celebrate whoever succeeds. #AAS233 pic.twitter.com/QYtYMCojcz

— Grant Tremblay (@astrogrant) January 8, 2019

Special Session: AAS WorldWide Telescope in Outreach and Education (by Stephanie Hamilton)

Screenshot of the WorldWide Telescope web client. [WWT]

• Astro 101 courses (Pat Udomprasert, on behalf of Ned Ladd and Stella Offner): To explain parallax to his students, Ladd designed a laboratory exercise in WWT that exaggerates the shift in background stars caused by Earth parallax motion. By examining the parallax shift of the Big Dipper’s stars from Earth, and from 6 light-years away from Earth, the parallax shift is much more evident.
  Offner uses WWT to create tours that accompany or preface her lectures. Further, her students design and narrate their own tours as course projects, rather than writing papers. These tours are all available online.

• Online courses (Jais Brohinsky): Lost Without Longitude through HarvardX uses WWT to explore how people historically used the night sky to situate themselves and predict where they were going. Additionally, using handmade telescopes, he and his students replicated Galileo’s measurements of Jupiter’s moons. They could then enter the measurements into WWT and evolve the Jovian system to watch the measurements match up with computed positions of Jupiter’s moons.

• Planetaria (David Weigel): With WWT, Wiegel brings in the latest astronomical data to share with the public and produce new planetarium shows on the same day. The Samford University planetarium hosts a summer program in which students create their own tours in WWT that can be shown to family and friends and exported to YouTube. WWT Version 6.0 will be compatible with the leading planetarium show software programs, making WWT tours a natural way to produce a show.

• K-12 curriculum (Harry Houghton): The NSF-funded initiative ThinkSpace uses WWT to reimagine middle school astronomy curriculum and help students develop spatial reasoning skills. WWT’s capability to shift perspectives (e.g. from Earth-based to space-based) allows students to visualize astronomical phenomena in different ways. In one example, Houghton asked Boston students to describe the path of the Sun on the winter solstice — most students replied that it rises due east and sets due west. By watching the Sun’s path in WWT and then shifting perspectives to view the Earth from space, students can see why the Sun’s path is what it is.
• Online public outreach (Robert Hurt): WWT can turn an otherwise flat webpage into an interactive learning experience. AstroPix, where images from major observatories are collated in one place, includes a link to WWT in the info pages of images with location information. WWT has also been used with large image data releases to make the data easily accessible while providing context.

So happy to be here watching WWT Ambassadors Project Director Pat Udomprasert sharing ⁦@AASWWT⁩’s outreach and educational features with a packed room at #aas233 https://t.co/u76inlNTYL pic.twitter.com/nXYZ6aprgr

— Alyssa A. Goodman (@AlyssaAGoodman) January 8, 2019

Press Conference: The Sloan Digital Sky Survey Keeps Going and Going (by Mia de los Reyes)

The Sloan Digital Sky Survey (SDSS), an ambitious project to measure the spectra of objects across most of the night sky, first started in 1990. Nineteen years later, it’s still going strong. Huge technological and scientific strides have been made, and today’s press conference caught us up with some of SDSS’s newest advancements.

Karen Masters (Haverford College), the spokesperson for SDSS-IV, started us off with an overview of SDSS. SDSS has accomplished most of its science goals through fiber spectroscopy. Thousands of optical fibers are plugged into large metal plates, and each fiber aperture obtains a single spectrum. Such a massive undertaking has required not only time and expertise, but money: Masters noted that SDSS is primarily funded by member institutions (71.4%) and the Sloan Foundation (24%). The US government (through the Department of Energy) provides very little of SDSS’s funding.

Masters then promoted the major SDSS projects. For instance, SDSS-IV MaNGA is the largest integrated field unit (IFU) survey in the world, providing spectra at every pixel within thousands of galaxies. SDSS-IV APOGEE is the world’s only stellar spectroscopic survey taking data in both hemispheres. Finally, SDSS-IV eBOSS, a survey mapping the spatial structure of galaxies in the universe, is scheduled to finish observing in Feb 2019. Soon, the next phase of SDSS will begin: SDSS-V will start “panoptic” spectroscopy with robotic (rather than human) fiber placement!

It’s Never too Late to be Active: APOGEE Chemical Abundances of the Large Magellanic Cloud Reveal a Lazy Past and Active Present

Next, David Nidever (Montana State University) discussed some of the results from the APOGEE survey. APOGEE recently expanded, building a spectrograph in the Southern Hemisphere that allows it to observe two very special galaxies: the Large and Small Magellanic Clouds (LMC and SMC), the Milky Way’s two largest and closest satellites.

The Large and Small Magellanic Clouds, photographed above Las Campanas Observatory in Chile. [Ryan Trainor (Franklin and Marshall College)]

The oldest stars in the LMC and SMC had very low alpha/iron ratios, suggesting that the Magellanic Clouds had very low star formation rates at early times. However, younger stars showed an uptick in alpha/iron, suggesting that the star formation of the LMC and SMC increased by about 6 times around two billion years ago — perhaps an indication of recent interactions with each other! This is just one of the interesting science results that APOGEE has uncovered. Press release

Science in the Library: A New Library of Stellar Spectra

Renbin Yan (University of Kentucky) then described the first release of the MaNGA stellar library (MaStar). A galaxy spectrum is primarily composed of a combination of stellar spectra, so to understand what’s happening in the galaxy you need to be able to understand what the individual stellar spectra look like.

H-R diagram containing all of the stars currently in the MaNGA Stellar Library. [SDSS collaboration]

Mining MaNGA for Mergers: Accurate Identification of Galaxy Mergers with Imaging and Kinematics

Finally, Rebecca Nevin (University of Colorado Boulder) discussed one of the science applications of SDSS. Galaxy mergers are important steps in galaxy formation and evolution, but identifying them can be difficult. By running simulations of mergers and producing mock SDSS images, Nevin is building a “more complete photo album” of different merger stages. This allows us to identify merging galaxies in SDSS images much more accurately than before.

Nevin plans to go even further using SDSS data. Some galaxy mergers don’t look like obvious merging systems in optical SDSS images. Fortunately, with the release of MaNGA observations, stellar velocities within galaxies can be mapped! These kinematic data can help identify these “hidden” mergers. Press release

Plenary Talk: RAS Gold Medal Lecture: Ripples from the Dark Side of the Universe (by Mike Zevin)

Sir James Hough presents on early gravitational-wave detectors.

In the next plenary talk, Sir James Hough from the University of Glasgow presented the RAS Gold Medal Lecture (the RAS gold medal is an honor that has also been shared by Edwin Hubble, Albert Einstein, Arthur Eddington, and Vera Rubin). Hough worked on GEO 600, a gravitational-wave interferometer that helped pave the way for the historic detections of gravitational waves over the past few years. Though smaller (and thus less sensitive) than its LIGO and Virgo siblings, GEO 600 offered the opportunity to test innovative technologies that allowed the unparalleled sensitivity of the interferometers that detected the first gravitational-wave signals.

Hough started his talk by covering the history of gravitational-wave detectors. He joined the field shortly after the first experiments designed to detect gravitational waves were in operation — aluminium bars that were designed to detect strains in space from passing gravitational waves. Though the famous Weber bars claimed to detect the effect of gravitational waves in the late 1960s, no similar experiments were able to replicate their findings and these claimed detections were shortly dismissed. Laser interferometry then became the hot option for gravitational-wave detection; development and testing progressed through the 1970s and 1980s. Hough noted that one of the most important steps forward was a 100-hour “coincident” run (i.e., two laser interferometers running at the same time) that took place in 1989 (though the results of this run weren’t published until 7 years later in 1996; pioneering science is a tough business). This proved that laser interferometers could run for long periods of time simultaneously, a necessity for the detection of gravitational waves.

The finance world takes notice of gravitational waves.

These early tests led the way for modern gravitational-wave interferometers. GEO 600 was developed and became a testbed for technologies used by larger laser interferometers. In particular, Hough worked on innovative silica suspension systems that isolated the detectors from vibrations so that they could be more sensitive to passing gravitational waves. These technologies were a vital component that allowed LIGO to be sensitive enough to make the first detection of gravitational waves in September 2015. These detections provided a “wealth” of knowledge, even enough to be noticed by the finance world.

Hough then outlined the future of the field — more interferometers are planned to join the network in the next decade such as KAGRA in Japan and another LIGO detector planned to be built in India. Looking even further into the future, “third generation” detectors such as the Einstein telescope and Cosmic Explorer will utilize the technologies he helped to develop with larger, more powerful designs to have an even better view of the gravitational-wave universe. These detectors will be able to observe merging black holes out to a redshift of 100 — mergers that occurred when the universe was only 2 billion years old. In closing, when asked about pursuing high-risk science like gravitational-wave detectors in their infancy, Hough advised young scientists to “Do what interests you and keep at it, don’t be talked into working on a field that you’re not interested in because you won’t enjoy it.”

Plenary Talk: HEAD Bruno Rossi Prize: Cosmic Rumbles and Fireworks from Merging Neutron Stars (by Kerry Hensley)

Colleen Wilson-Hodge (NASA/Marshall Space Flight Center) and the Fermi Gamma-ray Burst Monitor team were awarded this year’s High-Energy Astrophysics Division Bruno Rossi Prize, awarded annually “for a significant contribution to High Energy Astrophysics, with particular emphasis on recent, original work.” The Gamma-ray Burst Monitor (GBM) is one of the two Fermi instruments (the other is the Large Area Telescope), consisting of 14 individual detectors spanning an energy range from 8 keV to 40 MeV. As the name suggests, the Gamma-ray Burst Monitor detects gamma-ray bursts (GRBs), which signal the formation of a black hole.

Wilson-Hodge shows that @NASAFermi has been very busy finding various flashes of X-rays. #AAS233 pic.twitter.com/z0j5fHtJca

— Peter Edmonds (@PeterDEdmonds) January 9, 2019

GRBs can be divided into two classes: short gamma-ray bursts (SGRBs) lasting only a few seconds and long gamma-ray bursts (LGRBs) lasting tens to hundreds of seconds. SGRBs are indicative of two neutron stars merging, while LGRBs point to a massive star undergoing core collapse.

The gamma-ray counts seen by Fermi and the gravitational-wave strain seen by LIGO as a function of time. The GRB trails the merger by only seconds. (NASA’s Goddard Space Flight Center, Caltech/MIT/LIGO Lab)

The August 17, 2017, gravitational-wave signal — GW170817 — was quickly followed by an SGRB, which was detected by Fermi before the team was notified of its existence by LIGO. The spectral properties of the SGRB (known as GRB 170817A) were normal, with the exception of a weak low-energy tail that had never been seen before. Additionally, GRB 170817A was very dim — 2–3 magnitudes dimmer than other SGRBs with known distances.

While GRB 170817A came with surprises, it also conformed to many predictions about neutron star mergers and helped us explore some exciting science. Notably, the combined observations of GW170817 and GRB 170817A allowed us to measure the speed of gravity — and we found that it’s equal to the speed of light to within one part in a quadrillion! These observations also allowed us to constrain the maximum mass a neutron star can have before collapsing into a black hole and to learn more about how SGRBs are produced.

There are still some big questions left to be answered. Dr. Wilson-Hodge is especially excited for the first unambiguous detection of a neutron star–black hole merger. Another lingering question is whether or not a black hole–black hole merger is accompanied by a GRB. Theory says not, since there’s no matter around to generate the electromagnetic radiation, but the tentative correlation observed between a gravitational-wave signal (GW150914) and a GRB might indicate otherwise. We need more detections to learn more! If we assume that GW150914 was associated with a GRB, models suggest that anywhere from 1 in 3 to 1 in 100 black hole–black hole mergers will have an associated GRB. Stay tuned for this and more exciting discoveries to come at the confluence of gravitational-wave and gamma-ray astronomy!

Wilson-Hodge gives a summary of future science with NS-NS mergers & then discusses the fascinating possibility of a gamma ray signal from the first black hole-black hole merger. That needs more testing. #AAS233 pic.twitter.com/K4Q6yWtAY3

— Peter Edmonds (@PeterDEdmonds) January 9, 2019

Special Session: SOFIA Town Hall (by Susanna Kohler)

What’s the latest news from our favorite airborne infrared telescope? We went to the SOFIA town hall to find out.

We’re hanging out at the @SOFIAtelescope town hall to get the latest news from this unique observatory. #AAS233 pic.twitter.com/CfQTeQJocM

— astrobites (@astrobites) January 9, 2019

SOFIA — the Stratospheric Observatory for Infrared Astronomy — is a 2.7-m telescope that’s mounted in the back of a 747 jetliner. When SOFIA flies in the stratosphere, a garage-door-sized door opens up in the back of the plane and the telescope points out the side.

Why construct such an unusual observatory? SOFIA has many of the advantages of a space observatory: it flies above almost all the water vapor in the Earth’s atmosphere, which would otherwise block the infrared emission it observes. Unlike space telescopes, however, instruments mounted on the SOFIA telescope can be easily repaired, upgraded, and exchanged. The instrument installed on SOFIA is, in fact, swapped out every few weeks in order to maximize possible science, based on demand from accepted observing proposals from the scientific community.

In his broad overview of recent SOFIA activities, Director of Science Mission Operations Harold Yorke touched on some of the challenges that the airborne observatory faced in the last observing cycle. Besides the standard weather concerns ordinary observatories must juggle, SOFIA has problems like leak repairs and sluggish throttles that can cut into observing time. In spite of these challenges, York reported that they had made up most of the time in the most recent observing cycle.

The biggest challenge SOFIA faces at present is, of course, being grounded due to the government shutdown. The observatory had been slated to visit the Boeing field here in Seattle during the AAS meeting, so that astronomers could have the rare opportunity to interact with the observatory in person. The shutdown, however, forced SOFIA to remain in California, with the team anxiously awaiting the go-ahead to begin mission operations once more.

From SOFIA town hall at #AAS233: SOFIA observing flights are grounded because of ongoing government shutdown. Once shutdown ends, it will take about a week to resume flights. Will be lost flight opportunities in current observing cycle (Cycle 6) as a result.

— Jeff Foust (@jeff_foust) January 9, 2019

That signal can’t come soon enough for scientists whose proposals have been accepted for the current and future observing cycles; science can’t be conducted when the plane is grounded, and SOFIA runs a tight schedule that is unlikely to allow for missed observations to be made later in the year.

Nonetheless, the team remains hopeful about the future; SOFIA’s observations continue to lead to new and important scientific discoveries, and we’re all eager to see what will be found next!