Cat's Eye nebula

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

exoplanet radius v mass

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 radiiall exoplanets below this limit are rocky planets.

catalog of spectra

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! 

Press Conference: Galaxies Weird & Wonderful (by Haley Wahl)

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.

lopsided satellite distribution

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

hot circumgalactic medium

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.

decadal diversity

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. 

HST publication rates

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.

HST publication rate

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 postdoc

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.

Astrophysics Research by the Numbers

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 Missions in the works

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

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.

planetary nebulae

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. 

accreting pulsar

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

pSCT crab detection

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.

BH Growth

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. 

galactic center

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?

molecular excitation

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. 

centers of galaxies

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 236

This week, AAS Nova and Astrobites are attending the first-ever virtual American Astronomical Society (AAS) meeting.

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!

astrobites at AAS 236

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.

AAS 236 lobby

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.

Meet the AAS Keynote Speakers: Dr. Dara Norman
Meet the AAS Keynote Speakers: Dr. Lisa Kaltenegger
Meet the AAS Keynote Speakers: Dr. Jo Dunkley
Meet the AAS Keynote Speakers: Prof. James Lowenthal
Meet the AAS Keynote Speakers: Prof. Paola Caselli
Meet the AAS Keynote Speakers: Prof. Sandra Cruz-Pol
Meet the AAS Keynote Speakers: Dr. Jackie Faherty
Meet the AAS Keynote Speakers: Dr. Kazunari Shibata
Meet the AAS Keynote Speakers: Dr. Christy Tremonti
Meet the AAS Keynote Speakers: Prof. Elisabeth Mills

AAS 236 plenary speakers


AAS Publishing

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

Wednesday, 3 June, 12:00–12:10 pm EDT, Simon Newcomb room. View the abstract here.
If you are signed in as a meeting attendee, you can view the iPoster here.

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.

Laboratory Astrophysics, Instrumentation, Software, and Data corridor

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.

astronomical software

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!

Murchison Widefield Array

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.

Chris Lintott

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. 

TW Hya

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. 

Parker Solar Probe

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

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

Lensed Quasars

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

K dwarfs

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)

In this special session, we get a taste of some planetary science, thanks to the New Horizons Kuiper Belt Extended Mission team. They report on the scientific results from the spacecraft’s 2019 flyby of Kuiper Belt Object (KBO) 2014 MU69, now formally known as Arrokoth. 


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]

Press Conference: Astronomy Confronts Satellite Constellations (by Aaron  Tohuvavohu)

[Coming soon!]

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

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.

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.

EHT 2017 campaign

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.”


Swan Nebula

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)

Bergin plenary

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:

  1. The planet must be rocky.
  2. The planet must be the correct distance from its host star for liquid water to exist.
  3. 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.

Protoplanetary disk

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)

radcliffe wave

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

price-whelan 1 star cluster

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. 

fast radio burst

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. 

NGC 1559

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.

NGC 3766

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!

Van Saders plenary

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 workshop leaders

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.

Astrobites workshop

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.

LIGO Livingston

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

FRB 180916

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

M87 jet

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

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.

anatomy of the Milky Way

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.

TOI 700

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

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

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.

Kalili plenary

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. 

Metzger plenary

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.

Kasen plenary

Dan Kasen, a co-awardee of the HEAD Bruno Rossi Prize, schematically showing the blue and red components of a kilonova explosion.

UGC 2885

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.

Kavli Foundation Plenary Lecture: Black Holes Snacking on Stars: A Systematic Exploration of Transients in Galaxy Nuclei (by Mike Zevin)

In the kickoff plenary of #AAS235, Suvi Gezari (University of Maryland) got us ready for breakfast by illuminating the stellar snacks of black holes. Just like how the tidal forces of the Moon stretch and squeeze the Earth (giving us, for example, high and low tides on Waikiki beach), black holes exert tidal forces on stellar bystanders. Particularly unlucky stars can be ripped apart entirely by the black hole, leading to a so-called tidal disruption event (TDE). This happens when a star enters the black hole’s tidal disruption radius, which is dependent on the star’s size and the relative mass between the star and black hole. Since the tidal disruption radius of a star is a direct probe of the black hole mass, observations of such events can tell astronomers about the black hole that was responsible, as well as properties of the star that was disrupted itself.

Tidal Disruption Event
Figure 1: An illustration of a tidal disruption event. As the star approaches the black hole, it gets torn apart by the gravitational forces and accretes around the black hole. [NASA/CXC/M.Weiss]

Behemoth black holes, larger than about 100 million solar masses, will swallow stellar interlopers entirely before they can be ripped apart. This is because the tidal disruption radius of the black hole is inside the black hole’s event horizon (i.e., where no light can escape). However, TDEs are an excellent probe for lighter supermassive black holes, as well as the infamous and elusive intermediate-mass black holes. Gezari described how observations of TDEs are excellent probes for lower-mass supermassive black holes, allowing astronomers to better probe the coevolution of black holes and lower-mass galaxies.

Gezari highlighted the wide range of efforts across the electromagnetic spectrum that contribute to the detection and characterization of TDEs, and how the discovery of these transients has been propelled forward by optical wide-field time domain surveys. High cadence surveys such as ASAS-SN and Pan-STARRS can characterize the optical evolution of these rapidly-evolving transients in great detail, and are excellently complemented by observations in higher-energy ultraviolet and X-ray observatories such as Swift. Gerazi discussed some of the recent surprises of TDE science, such as multiple populations of TDEs separated by their emission temperature and spectral characteristics, as well as the lack of TDE observations in young blue galaxies. Gerazi then stressed how current (e.g., ZTF) and future (e.g., LSST) wide-field time domain surveys will produce an avalanche of TDE candidates to help better our understanding of these interesting transient events and the black holes responsible for them, and identifying TDE candidates from the plethora of transients is of utmost importance. She closed her plenary by overviewing a handful of ZTF TDE discoveries, which her team conveniently nicknamed after Game of Thrones characters…make sure to beware of Joffries!

ZTF18abdfwur, a.k.a. a “Joffrey”, an example of a Type Ia supernova masquerading as a TDE.

Press Conference: Galaxies & Their Black Holes (by Susanna Kohler)

The first press conference of the meeting opened on large scales, discussing some of the latest things we’ve learned about massive black holes and galaxies.

We know that nearly every large galaxy hosts a central supermassive black hole weighing millions to billions of solar masses. But do dwarf galaxies have equivalently massive tenants? Amy Reines (Montana State University) and collaborators used high-resolution Very Large Array observations to go on a hunt for radio-bright black holes in dwarf galaxies — with great success! The team found a total of 13 massive black holes — they estimate these probably weigh around 400,000 solar masses — in dwarf galaxies in their survey. Intriguingly, not all of them are located in their galaxies’ centers; many are instead wandering around the outskirts of their hosts. Reines and collaborators suggest this is likely due to recent interactions and mergers that kicked these black holes out of the galaxies’ centers. Unlike in large galaxies, where the supermassive black holes are heavy enough to quickly sink back to their galaxies’ centers, these dwarf-galaxy black holes take longer to settle back down. Press release

In keeping with the theme of galaxy interactions and mergers, Ezequiel Treister (Pontificia University Católica de Chile) next presented on new observations of NGC 6240, a merging galaxy system located 400 million light-years away from Earth. Since this system is still in the process of merging, it still has two nuclei, each containing a supermassive black hole. The new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed a bridge of cold molecular gas that stretches between the two supermassive black holes, fueling them as the galaxies collide. We’re super lucky to have captured this moment, since the bridge of gas is a transient structure that will likely only last around 10 million years — the blink of an eye in galactic timescales! In about 2 billion years, the nuclei will have merged, and the final result will be a massive elliptical galaxy with a single black hole. Press release


In 1980, astronomer Vera Rubin measured the rotation of the spiral galaxy UGC 2885, providing evidence for a large amount of dark matter in this galaxy. Now, Benne Holwerda (University of Louisville) and collaborators have used the Hubble space telescope to image this galaxy in high detail (see the cover image at the top of the page), further exploring the structures of this gentle giant. UGC 2885, nicknamed “Rubin’s Galaxy”, is one of the largest known galaxies in the nearby universe, clocking in at 2.5 times wider than the Milky Way and with 10 times the number of stars. Scientists are still working to understand how a galaxy is able to grow to this enormous size. Press release

When was the last time a hydrogen atom did anything interesting on a Saturday night, like going to a party and getting ionized? James Rhoads (NASA Goddard Space Flight Center) points out that, for a typical atom, the last time anything interesting happened was during reionization, a period of time between 150 million and one billion years after the Big Bang. Using the Cosmic DAWN Survey, Rhoads and collaborators discovered EGS77, a group of galaxies from just 680 million years after the Big Bang that contains some of the first stars that formed in the universe. The observations show overlapping bubbles of ionized gas around these early galaxies — signs of the start of reionization, which ultimately cleared the way for light to travel through our universe. Press release

Plenary Lecture: He Lani Ko Luna, A Sky Above: In Losing the Sight of Land You Discover the Stars (by Kate Storey-Fisher)

Father-daughter speakers Kālepa Baybayan and Kala Baybayan Tanaka led us on a seafaring journey in their plenary talk. As navigators with the Polynesian Voyaging Society, Baybayan and Tanaka use the stars for navigation by sea, tapping into indigenous astronomical knowledge and traditions.

Baybayan began by telling the story of humanity spreading across the globe, first by land and later by sea. Around 4,000 years ago, the first seacraft was developed, and the art and science of navigation was born. One seafaring community, the Lapita, spread from Southeast Asia to archipelagos throughout the Pacific, leaving behind a trail of broken pottery that allowed researchers to trace their trajectory.

In the early 1970s, the Polynesian Voyaging Society was established, and they set out to demonstrate indigenous navigation practices. Baybayan was captain of the Hōkūleʻa, a historically accurate Polynesian canoe, which set out from Hawaiʻi in 1976. Using only Polynesian navigation techniques, the voyagers navigated to Tahiti in 33 days. The navigation system relies on astronomy, meteorology, and mathematics — the same foundations as those used today.

The arrival of Hōkūleʻa, a reconstruction of a traditional Polynesian voyaging canoe, in Honolulu from Tahiti in 1976. [Phil Uhl]

Tanaka became hooked on sea navigation as a high schooler after a 24-hour voyage with her father. She learned to use the swells and the stars as guides, and even to recognize the sound of the breathing of dolphins swimming alongside them. In 2013, she participated in the Mālama Honua Worldwide Voyage, in which over 245 voyagers circumnavigated the globe (in many legs) to educate communities on living sustainably. Together they traveled 60,000 nautical miles and visited 150 ports. Tanaka now educates young people on the stellar compass and the history of voyaging.

Bayaban and Tanaka concluded with an emphasis on the science that grounds their work. They use the same star maps as astronomers — just labelled with the stars’ Hawaiʻian names.

 Kala Baybayan Tanaka presentation
Kala Baybayan Tanaka speaks about her experience as a voyager with the Polynesian Voyaging Society.

Press Conference: TEAM-UP for Physics & Astronomy (by Ellis Avallone)

The second press conference of the meeting took a different turn. Instead of discussing discoveries of astrophysical phenomena, a task force from the American Institute of Physics (AIP) reported on findings in a recent report on “Elevat[ing]African American representation in physics and astronomy.”


The CEO of AIP, Michael Moloney, opened by introducing the motivation for compiling this report. He stated that over the past decade the number of physics students graduating with physics bachelor’s degrees had doubled, but the number of African American students had stayed roughly the same. The AIP sought to find out why.

Next, Edmund Bertschinger (Massachusetts Institute of Technology), co-chair of the task force organized to address this disparity, discussed the framework of their study and how it was conducted. The “Task force to Elevate african AMerican representation in Undergraduate Physics & astronomy”, or TEAM-UP, conducted surveys of students and faculty, in-person interviews of African American students, and on-site visits to institutions that did an exceptionally good job of retaining and graduating African American students. TEAM-UP also recruited social scientists to the task force to assist with data interpretation. It’s also important to note that these data were interpreted under the assumption that “African American students have the same motivation and intellect as students in other racial groups.”

Bertschinger also outlined several ways in which this report stands out from previous reports on retaining minoritized students in STEM. To start, this report examines the practices in physics and astronomy in particular, and not just academia as a whole. The report also focuses heavily on the culture of the field, and the ways in which that culture is detrimental to African American students. Finally, this report discusses recommendations for addressing these issues and creating long-lasting change within departments. These recommendations were informed by practices at model institutions with high retention rates of African American students.

Finally, Jedidah C. Isler (Dartmouth College) introduced several of these recommendations. Isler began by thanking the students who were involved in the report, as they were the group who are being most affected. One recommendation seeks to address the fact that African American students tend to doubt themselves in the classroom far more than others. “That is ubiquitous in their experience,” says Isler. “If you can get students to feel confident in [the classroom]they feel like they belong.” The report emphasized the importance of “counterspaces”, places of refuge from academic spaces where students can feel welcomed. Departments need to become aware of these spaces, and actively seek out these spaces for students who need support. Additionally, faculty need to set norms for both the classroom and departments and have a responsibility to mitigate and prevent exclusionary behavior. Press release.

Press Conference: Seminar for Science Writers: Hubble @ 30 (by Briley Lewis)

Hubble during the 2009 servicing mission. [NASA/Hubble]

Launched in April 1990, Hubble is still in good shape despite its age. Jennifer Wiseman (NASA Goddard SFC) gave an overview of Hubble’s impressive history, noting major discoveries such as verifying the existence of dark energy and the first characterization of an exoplanet atmosphere. It has answered new questions and made new observations that weren’t anticipated at its inception, such as detecting radiation from a gravitational wave source. Thanks to multiple servicing missions (the most recent in 2009), the telescope and its instruments have been not only maintained but also upgraded. Wiseman claims that the telescope is at its “peak of scientific return”, with over 1,300,000 observations completed and 15,000 papers published using Hubble data.

Artist’s impression of the TRAPPIST-1 planetary system
This artist’s impression shows the view from the surface of one of the planets in the TRAPPIST-1 system. [ESO/N. Bartmann/spaceengine.org]

One of the unanticipated uses for Hubble is to study exoplanets; Nikole Lewis (Cornell University) aptly pointed out that “the field of exoplanet science is younger than the HST.” After the Nobel-winning discovery of 51 Pegasi b in 1995, HST observed sodium in the atmosphere of exoplanet HD209458 b, pioneering the technique of transmission spectroscopy. Using its valuable ultraviolet-sensing capabilities, it revealed atmospheric escape on exoplanets, and in recent years HST has been valuable in follow-up of habitable-zone worlds such as TRAPPIST-1 and K2-18b. Going forward, HST will still have a valuable role as our important window into the ultraviolet and visible, complementary to the infrared capabilities of the James Webb Space Telescope.

Looking closer to home, Hubble has also been valuable in our own solar system, serving as critical support for in situ missions. Heidi Hammel (Association of Universities for Research in Astronomy) explains how it gave us global context and dust storm warnings for observations from Mars missions; discovered four moons around Pluto and found New Horizons’ second target, the Kuiper Belt Object MU69; and studied aurorae on giant planets like Jupiter (where the Juno mission is currently orbiting). Recently, Hubble even captured images of the first interstellar comet, 2I/Borisov. According to Hammel, what makes Hubble unique in the solar-system domain is its ability to do multi-decade, multi-wavelength, multiple-object studies, making it complementary to shorter-lived, specific space missions.

Lastly, Garth Ilingworth (UC Santa Cruz) brought us back to the big picture, discussing Hubble’s pioneering deep field images. Starting with the first Hubble Deep Field (HDF) in 1995, the telescope has produced successively more impressive images such as 2009’s Hubble Ultra Deep Field (HUDF09) and 2012’s Extreme Deep Field (XDF). The XDF is the culmination of 23 days of exposure from 800 orbits, 2,963 images taken over a span of 10 years. It detects distant galaxies up to 13 billion years ago, covering 97% of all time.
Images like these are part of what have secured Hubble’s lasting legacy, not only in science but also in popular culture. Ray Villard (STScI) remarked on Hubble’s legendary status, known as a household name and referenced in many forms of popular media, in part thanks to 1,000+ press releases based on the telescope’s data. According to this panel, HST should have a bright future ahead still, with NASA committed to funding it as long as it is “scientifically productive.” Scientists are already preparing for complementary observations to JWST and future missions, and although HST will de-orbit eventually, it seems that day should hopefully be far away.

Hubble Extreme Deep Field
The Hubble Extreme Deep Field (XDF), assembled from 10 years of Hubble data, covering a swatch of sky similar in size to the full Moon. [NASA]

HAD LeRoy E. Doggett Prize Lecture: From the Invention of Astrophysics to the Space Age: The Transformation of Astronomy 1860-1990 (by Mike Zevin)

For the next plenary lecture, Robert W. Smith (University of Alberta) took us on a trip back through time to examine the evolution of astronomy and astronomers over the past 150 years. According to many prominent mid-19th-century astronomers, astronomy was regarded as the study of the motion of the heavenly bodies. The natural laws that governed the motion of these bodies was already set out; progress in astronomy was reliant solely on making more precise measurements. Because of this, there was not thought to be much room for new discovery. Smith argued that one of the reasons that countries were still pouring money into constructing massive observatories was to display national prowess.

With the advent of the spectrogram, astronomers in the 1860s such as Sir William Huggins began to dissect the light coming from stars and nebulae, giving birth to the field known as astrophysics. However, Smith pointed out that early astrophysicists were not like the astrophysicists that would emerge later. In scientific texts, stars were described as objects designed to fit the special purposes of living beings on worlds going around them, a very theological view. This philosophy had a paradigm shift not because of any astronomical theory, but rather because of the theory of evolution. The story thus shifted from one of natural theology to scientific naturalism — rejecting religious input into scientific research.

Mt. Wilson Solar Telescope
The Snow Solar Telescope, the first telescope installed at the fledgling Mount Wilson Solar Observatory. [AAS Nova/Susanna Kohler]

Smith then turned to the 20th century, where astronomy saw an increase of professionalism and less room for amateur astronomers to make a substantial scientific impact. Due to millionaires like Carnegie showing strong interest in astronomy (and funding massive observatories such as Palomar, Terkes, and Mt. Wilson), the US became a leading power in observational astronomy. With the rise of photography, new opportunities were also available for underrepresented communities in the field. Women astronomers, for example, were able to move out of the “domestic sphere” (i.e., could only work as an astronomer if they were married to an astronomer). The standard example of this is the group of Harvard Computers, though a number of other such groups appeared in the early 1900s. In the 1930s, astronomy encountered a great divide: the “one-galaxy universe” view and the “many galaxies all expanding away from another in a vast universe” view, which Smith said challenged what astronomers regarded as the realm of science versus the realm of metaphysical. Smith closed with how, thanks in part to the Cold War, the field astronomy became much more political, which was necessary for projects like the Hubble Space Telescope to come to fruition after its conception in the 1970s.

Henry Norris Russell Lecture: Intriguing Revelations from Lithium, Beryllium, and Boron (by Tarini Konchady)

This plenary was given by Ann M. Boesgaard (University of Hawaii), this year’s winner of the Henry Norris Russell Lectureship. Boesgaard received the award for “her pioneering, sustained work in using light-element abundances to test Big Bang nucleosynthesis and to probe stellar structure and stellar evolution”.

cosmic rays
Artist’s impression of the shower of particles caused when a cosmic ray, a charged particle often produced by a distant astrophysical source, hits Earth’s upper atmosphere. [J. Yang/NSF]

Boesgaard focused on the three elements in her talk, specifically lithium, beryllium, and boron. These three elements are oddly rare in the universe, and it took the second half of the 20th century to figure out why. Some amount of lithium was formed in the Big Bang, but it wasn’t enough to explain the abundances of lithium observed in stars. The famous 1957 B2FH paper (written by Margaret Burbidge, Geoffrey Burbidge, William A. Fowler, and Fred Hoyle) laid out how most of the elements were created in stars but the creation of lithium, beryllium, and boron was attributed to a mysterious unknown “x-process”. The x-process turned out to be “galactic cosmic ray spallation” — the phenomenon of cosmic rays breaking down heavier elements into lighter elements.

With the creation problem solved, Boesgaard pivoted to how the destruction of these light elements can help us probe stellar structure. This is where spectra do the heavy lifting and where Boesgaard provided some anecdotes on how astronomy was done in the age of photographic plates (as opposed to today’s charge-coupled devices, or CCDs). Two star clusters came up repeatedly — the Hyades, which is ~650 million years old, and the Pleiades, which is ~100 million years old.

In the Hyades, when plotting lithium abundance versus temperature, a dramatic dip, rise, and falloff are seen. This is absent in the Pleiades, suggesting that whatever process is destroying lithium in stars happens over long timescales. When similar plots were made for beryllium and boron in both systems, a shallower dip was seen but a falloff was not.

The depletion of lithium, beryllium, and boron is likely due to these elements being dragged into the interior of stars and destroyed. However, the varying hardiness of the elements means that they are destroyed at different temperatures and layers within the star. Lithium is the fastest to be destroyed, followed by beryllium and then boron. The takeaway is that by examining the surface abundances of lithium, beryllium, and boron, we can probe the interiors of stars!

Boesgaard talk
The temperatures and inner stellar layers at which lithium, beryllium, and boron are destroyed (2.5 million kelvin, 3.5 million kelvin, and 5 million kelvin respectively).
astrobites aas 235

This week, we’re attending the American Astronomical Society (AAS) meeting in Honolulu, Hawai’i!

astrobites table

Astrobites authors talk to students at the undergraduate orientation at AAS 235 Saturday night.

Thanks to all of you who stopped by the Astrobites table at the undergraduate reception last night; we look forward to seeing you around at the rest of the meeting. If you’re at the meeting and missed us at the undergrad reception, please stop by and visit this week! You can find us at the AAS booth (#423) in the exhibit hall — we have sunglasses, stickers, pins, and more, so swing by to pick up some swag and say hi.

For anyone who’s missing the meeting, or for those attending who can’t make all the sessions you want to: Astrobites and AAS Nova are working together to report highlights from each day. You can follow along on astrobites.org or at aasnova.org; look for an update after each day of the meeting. If you’d like to see more timely updates during the day, we encourage you to search the #aas235 hashtag on twitter.

If you’re interested in reading up on some of the keynote speakers before their talks at the meeting, keep following along at astrobites.com … we’ll be posting interviews with speakers in advance of their keynote talks. Several of these interviews for AAS 235 have already been published; you can check them all out under the aas235 tag on astrobites.com. This is a great opportunity to learn more about prominent astrophysicists and the paths they took to get where they are today!

Lastly, if you’d like to come chat with the AAS publishing team, we’d love to see you at the AAS booth or at any of several events during the meeting:

  • Celebration of a new AAS/IOP ebook on astronomy education
    Sun Jan 5 during the 5:30 pm poster session (with free beer!)
    AAS Booth (#423)
  • AAS Publishing: What’s New
    Tues Jan 7 12:30-2:00 pm (with free lunch!)
    Convention Center 301B
  • AAS Publications Committee Meeting Open Session
    Wed Jan 8 2:00-4:00 pm
    Convention Center 305B
astronomy education ebook

The American Astronomical Society recently launched a new partnership with IOP to produce a series of ebooks about astronomy and astrophysics. One of the newest books in this line, Astronomy Education, Volume 1: Evidence-based instruction for introductory courses, is edited by University of Arizona professors Chris Impey and Sanlyn Buxner, and it’s now available for download with an institutional IOP ebook subscription.

Why Should We Care About Astronomy Education?

Any astronomer can (and should!) argue the importance of sharing our understanding of the universe with students. But astronomy education has a particularly unique role in undergraduate education: it’s one of the most popular subjects for non-science majors, and it often represents the last formal exposure to science for these students.

It stands to reason, then, that a well-taught introductory astronomy course can be enormously impactful. But what does it mean to teach an intro astronomy class well?

Where Astronomy Education Research Comes In

AER ebook cover

Cover of the new AAS/IOP ebook edited by Drs. Chris Impey and Sanlyn Buxner, Astronomy Education, Volume 1.

To address questions about student learning, we turn to the field of education research. In this field, scientists methodically explore different teaching techniques and conduct studies to determine what strategies are most effective when trying to achieve specific outcomes — like improving test scores, increasing retention, or maximizing student engagement.

This education research has established many evidence-based instruction methods and practices that can be used to improve undergraduate education — and these strategies, specifically as applied to undergraduate introductory astronomy courses, are clearly outlined in the sections of Astronomy Education, Volume 1.

What Can You Learn from Astronomy Education, Volume 1?

Central to the strategies discussed in this ebook is the idea of learner-centered teaching — an alternative to a lecture-based instruction format that instead encourages students to be active participants in their education. The authors of Astronomy Education, Volume 1 provide insight into many different aspects of learner-centered teaching, like how to create student buy-in, how to develop appropriate course materials, and how to measure the impact your teaching strategies are having.

Dr. Impey and Dr. Buxner’s informative book provides information and resources for those who are teaching intro astronomy for the first time, as well as for those who want to add to their toolkits and improve their students’ learning. Chapters in the book include:

  • Learner-Centered Teaching in Astronomy
  • Effective Course Design
  • Lecture-Tutorials in Introductory Astronomy
  • Technology and Engagement in the University Classroom
  • Using Simulations Interactively in the Introductory Astronomy Classroom
  • Practical Considerations for Using a Planetarium for Astronomy Instruction
  • Authentic Research Experiences in Astronomy to Teach the Process of Science
  • Citizen Science in Astronomy Education
  • WorldWide Telescope in Education
  • Measuring Students’ Understanding in Astronomy with Research-based Assessment Tools
  • Everyone’s Universe: Teaching Astronomy in Community Colleges
  • Making Your Astronomy Class More Inclusive

More Information

Astronomy Education, Volume 1 ebook download: https://iopscience.iop.org/book/978-0-7503-1723-8

If you plan to be at AAS 235 in Honolulu, HI, come by to celebrate the publication of Astronomy Education, Volume 1 and to meet Dr. Impey, Dr. Buxner, and many of the book’s contributors in person! We’ll be at the AAS booth (#423) in the exhibit hall on Sunday, 5 January at 5:30 p.m. during the poster session.

Keep an eye out in 2020 for Astronomy Education, Volume 2: Best Practices for Online Learning Environments, edited by Chris Impey and Matthew Wenger.

To learn more about the AAS/IOP ebook partnership and current and upcoming titles, visit http://iopscience.iop.org/book/aas.


Chris Impey and Sanlyn Buxner 2019. Astronomy Education, Volume 1: Evidence based instruction for introductory courses. doi:10.1088/2514-3433/ab2b42

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