Welcome to the virtual winter American Astronomical Society (AAS) meeting! Astrobites is attending the conference as usual, and we will report highlights from each day here. If you’d like to see more timely updates during the day, we encourage you to search the #aas237 hashtag on twitter. We’ll be posting once a day during the meeting, so be sure to visit the site often to catch all the news!
Royal Astronomical Society (RAS) Gold Medal in Astronomy: A Schematic Model for Black Hole Growth and Galaxy Quenching (by Haley Wahl)The first plenary of the fourth day of AAS 237 was given by Dr. Sandra Moore Faber (UC Santa Cruz), winner of the Royal Astronomical Society’s incredibly prestigious Gold Medal in Astronomy (previous winners of this medal include Albert Einstein and Stephen Hawking!), with her talk on black hole growth and galaxy quenching. Galaxy quenching is the process by which galaxies stop forming stars. Dr. Faber started off by showing the Hubble sequence and posing the major question of the talk: “How do galaxies stop forming stars?” Astronomers can predict the distribution of the mass of dark matter halos, inside which galaxies form and grow. But why do the dark matter halos keep growing but the galaxies inside them do not?
Dr. Faber focused her question on a specific kind of galaxy: middle-sized galaxies like our own Milky Way. In the current paradigm for these galaxies, their quenching is thought to be caused by feedback from accreting central supermassive black holes, and that feedback is ejective (e.g., by blowing out the gas), preventative (e.g., by heating up the gas), or both. Black holes grow at the centers of galaxies during their formation; the black hole has little effect when a galaxy is young and the black hole is small, but eventually the black hole becomes massive enough to affect the galaxy itself and cause its star formation to quench. It is possible that the growing black hole at the center of the galaxy affects the gas in the halo surrounding the galaxy and alters its ability to cool and fall in. There are a few unanswered questions in this process, such as what the rules are for black holes growing in mass, the nature of black hole feedback, how that feedback interacts with gas in the galaxy, the origin of black hole scaling laws, and what exactly happens when galaxies start to quench. There is a lot left to understand.
Scaling laws are extremely important for answering these questions. Dr. Faber related galactic scaling laws to the zero-age main sequence for stars, which, when understood, unlocked the sequence of nucleosynthesis and how stars shine. By understanding the equivalent scaling laws for galaxies, we can understand how they evolve and how their star formation quenches. She then presented five relations: stellar mass vs. halo mass, mass vs. star formation rate, galactic radius vs. stellar mass, central stellar density vs. stellar mass, and black hole mass vs. central stellar surface density. By examining all of these relations — and how they relate to each other — we can learn a lot about how galaxies are quenched. One very important aspect of this process is the boundary between star-forming and quenched galaxies, and what happens when a galaxy crosses it in a given relation, suggesting the conditions are right for quenching.
What causes this quenching boundary and why does it move? pic.twitter.com/TudLbeLwDF
— astrobites (@astrobites) January 14, 2021
These scaling relations are starting to reveal the nature of galaxy evolution, and how the different variables come into play. One interesting point we have learned from all this is that the connection between dark matter halos and black holes is incredibly tight. There are still many unsolved questions about galaxy quenching, but more advanced modeling is getting us closer to answering the question of how and why galaxies stop forming stars!
Live-tweeting of the session by Haley Wahl
Special Session: What to Expect Under a Biden-Harris Administration (by Briley Lewis)
This special session, composed of panelists with experience in a variety of science policy roles, was held to discuss “the upcoming presidential transition and what we can expect during the first months of the new administration.” Panelists included Joel Bregman (University of Michigan), Jack Burns (University of Colorado, Boulder), Dahlia Sokolov (no affiliation), and Mike Holland (University of Pittsburgh), and the panel was moderated by Joel Parriott (AAS Director of Public Policy) and Kelsie Krafton (AAS Bahcall Fellow).
Although President Elect Biden has assembled a transition team, the transition process has been slow to start due to resistance from the current administration. There are also many other committees and groups that deal with NASA, NSF, NIST, and the DOE: the House Committee on Science, Space, and Technology, the Senate Committee on Commerce, Science, and Transportation, the House and Senate Appropriation Committees, the House Committee on Energy and Commerce, and the Senate Committee on Energy and Natural Resources. The American Institute of Physics (AIP) also has tools for tracking the federal science budget and new appointments & nominations.
Since the transition team relies on advice from a number of parties, the AAS has already sent letters to the NASA transition team and the NSF transition team. Burns reported that he also made two recommendations to the transition team: don’t completely change the scientific agenda, and work on increasing the NASA budget to $25 billion (or at least avoiding cuts to NASA/NSF). Although changes in policy and priorities are to be expected for any change in administration, Burns emphasized that stark changes in scientific agenda creates uncertainty, both within NASA and with international partners, and impedes progress, saying, “Let’s build on infrastructure we already have in place.”
A participant brought up the question of how we can reduce this uncertainty, possibly creating mechanisms for longer-term commitments to projects and making it easier for international partners to commit and fund partnerships. Although multi-year appropriations are often suggested as a solution to this problem, the panelists emphasized that there is also a lot that scientists involved in major projects can do to increase stability, such as setting clear, stable science priorities, improving project management, and controlling budget overrun.
With another stimulus package likely coming soon, the panelists were asked how this spending would affect science. A certain amount of money should be allocated for “research recovery funds” (including a stimulus for NASA) and Sokolov commented that currently the biggest risk is not to the science goals, but to the pipeline of researchers. With postdocs in limbo, students unable to graduate, and hiring freezes, she expressed worry over a possible loss of talent. (The AIP has also put out information on how COVID-19 is affecting the sciences.) Science education is also likely to be an area of interest for the incoming administration, which has placed emphasis on diversity, equity, and inclusion, as well as affordability issues both at the undergraduate and the graduate levels.
The Endless Frontiers Act is a recently introduced piece of legislation from Sen. Chuck Schumer that proposes changes to the NSF. Someone in the Q&A session raised concern that if funding is split between basic and applied sciences without a significant increase in the overall budget, it would lead to a major decrease in basic science support. Although there is a “legislative firewall” built into the legislation, Sokolov warned that those measures can be essentially ignored by an appropriations committee, so this proposal needs careful consideration of how it would change normal NSF operations. Burns added that the NSF is governed by the National Science Board, which generally helps to moderate and implement changes to the agency.
Participants also questioned when the announcement of a new NASA administrator is expected. Although no timeline was given, the panelists expressed the hope for a choice sooner rather than later, and Burns stated that the administration is looking to hire the first woman administrator to NASA, with some very qualified names already put forward for the position. Additionally, panelists discussed the Artemis mission, tasked with landing “the first woman and next man on the Moon by 2024.” Burns expressed doubt that the 2024 goal would be met, calling it “very unlikely” since the budget doesn’t accommodate for developing human landing systems. However, he was hopeful that private companies would work on this goal, too, mentioning that Jeff Bezos and his company Blue Origin have stated that they will go to the Moon whether or not NASA does. In response, participants expressed concerns about private interests setting priorities for space exploration, mentioning the small satellite problems (which will be discussed further in a later session today!).
Press Conference: Galaxies & Quasars II (by John Weaver)
The first press conference of Day 4 of AAS 237 continued the theme from earlier — galaxies and quasars. Four scientists were featured in the hour-long conference, each presenting a different aspect of galaxy evolution.
First up was Adi Foord from Stanford University, who discussed her work on supermassive black holes. When galaxies collide, we can see what happens on large scales using optical and X-ray imaging. But what happens to the supermassive black holes that reside at their centers? In what’s known as the “final parsec problem”, theory predicts that pairs of inspiralling supermassive black holes may stall out, never getting close enough to merge. However, Dr. Foord points out, this problem is mitigated when there is a third black hole involved in the merger, due to the faster circularization of their orbits. Finding collisions of three galaxies, whose supermassive black holes may actually merge quickly, is therefore of interest. Dr. Foord and collaborators used SDSS imaging to pick a handful of promising galaxy triple mergers, and then used Chandra to locate the X-ray-bright black holes. They confirmed four probable double black hole mergers and one triple merger. They also found that the dust and gas in these merging galaxies is enormous, and it’s significantly higher in the group of galaxies with the triple black hole merger. Press release
— astrobites (@astrobites) January 14, 2021
Next in the line up was Duilia de Mello (Catholic University of America) to talk about the Deep Images of Mergers or DIM Project. She has teamed up with a group of amateur astronomers in Brazil who use their own telescopes to image galaxy mergers. The crazy part is that they have been able to combine their efforts to match images taken in space by Hubble! By spending longer (41 hours!) observing with common amateur telescopes using extremely broad filters, they are able to cheaply image extremely faint features of galaxies — in particular, the tidal and shell features surrounding spheroidal galaxies, which are typically associated with galaxies that have recently undergone a major merger. These images can help us to understand the chaotic lives of these galaxies. De Mello is now gearing up to conduct a massively larger campaign to image the faint features of many other galaxies using the awesome power of amateaur astronomers! Press releaseThe next talk was from Jordan Guerra Aguilera (Villanova University), who started us on the theme of magnetic fields in galaxies. Specifically, Jordan and his team studied the well-known Cigar Galaxy (M82) which is known for its amazing outflowing material. By using a combination of complex measurements, grounded in the science of polarimetry, they were able to not only estimate the magnetic field strength of M82 to be a whopping 1 milligauss, but also map out the entire extended magnetic field way beyond the edge of the galaxy. With this magnetic field map in hand, they were able to determine that material ejected from M82 will escape the magnetic field lines altogether. Press release
Continuing on the theme of magnetism was Alejandro Borlaff (NASA Ames Research Center) who discussed groundbreaking insight into the magnetic fields in the disk of the Whirlpool Galaxy (M51; see the cover image at the top of today’s post) using the HAWC+ instrument aboard NASA’s SOFIA observatory (the one that’s an airplane!). Previous studies of magnetic fields in galaxies explored how the magnetic field structure interacts with the filaments of gas, and in turn how that can affect or regulate star formation. However, these studies were done at bluer wavelengths that we can measure from the ground, and they mapped the magnetic fields of the diffuse gas and then assumed a similar behaviour from the cold molecular gas, from which stars can form. SOFIA is special because it flies at the edge of space, which means it can observe far-infrared light that is absorbed by our atmosphere. By directly measuring the magnetic field associated with the cold molecular gas, Dr. Borlaff and his team were able to identify differences between the magnetic fields of the diffuse and molecular gas, meaning that much of what we thought we knew about magnetic fields and star-formation will have to be re-written. Press release
NOIRLab Town Hall (by Gourav Khullar)
In this town hall, NOIRLab (the National Optical-Infrared Astronomy Research Laboratory) leadership discussed its missions, updates and future plans, with the session titled “Enabling Breakthrough Discoveries for a Diverse and Inclusive Community.” The mission statement of NOIRLab — which is the umbrella organization unifying all NSF night-time optical/IR facilities into one — is to enable discoveries with observatories, and to develop data products and services for an inclusive astronomy community. The organization wishes to be an agent of change in the community via their projects, facilities, and modes of engagement.
In this session, we heard updates from:
- Gemini Observatory (and their new networks to coordinate observations of target-of-opportunity events, and adaptive optics and radial velocity measurement instruments)
- Vera C. Rubin Observatory (and their operations, plans for first light in October 2022, and community engagement plans)
- Community Science and Data Center (CSDC; which will manage their new dual-anonymous proposal system, open-access time with Keck Observatory consisting of 40 nights over 4 years, and the Astro Datalab data query and analysis service)
- Mid-scale observatories (like CTIO in Chile and operations with its 4-m Blanco telescope, and Kitt Peak National Observatory and its new DESI survey).
For the fiscal year 2021, NOIRLab will prioritise bringing the DESI survey online, expanding imaging capabilities, strengthening relationships with local communities, and building a program to protect dark skies from light pollution and satellite constellations.
Plenary: Thermal-IR Astronomy: Progress & Future Prospects (by Abby Waggoner)The second plenary talk today was given by Chris Packham from the University of Texas, San Antonio. In the 1940s, Carl Seyfert identified bright, stellar-like objects at the centers of distant galaxies. We now know these bright sources of light are active galactic nuclei, or AGN. AGN are bright across the entire electromagnetic spectrum, and many astronomers believe this bright emission is caused by accretion from the disk and torus surrounding the AGN, as shown in the figure to the right. However, the exact relationship between the accretion disk and the black hole were not well understood. This plenary talk walked us through infrared imaging and modeling done by Dr. Packham and his collaborators to better understand the relationship between the central black hole and the surrounding accretion disk and torus.
Unfortunately, it is difficult to obtain a high enough resolution when observing AGN to fully understand the relationship between the torus and the black hole. It turns out, protoplanetary disks can be used as an initial guide to AGN physics. This comparison provides a new way of interpreting AGN physics, but there are many different types of AGN. For example, some have jets and some have scattered or transmitted light, while others do not. The one common component between all AGN is the presence of a dust molecular torus. This theory, known as the Uniform Theory, suggests that the torus plays a key role in the bright AGN emission. But, what exactly is that role? And what exactly does the torus look like?
To answer these questions, we turn to infrared astronomy. Light emission from the torus peaks in mid-infrared light (MIR), meaning the torus is easiest to observe in MIR wavelengths. Initial models, shown in the left figure above, from Pier & Krolik (1992) and Pier & Krolik (1993) suggested that the torus was a smooth and homogeneous distribution of gas and dust, but this model was unable to accurately match observations. Thankfully, Sptizer and Gemini provided the data needed! The data combined from these telescopes led to the Clumpy Torus model (shown in the right figure above), which suggests that the torus is full of lots of individual clouds, rather than a single continuous disk.
Now with high resolution images and an accurate model of the torus, Dr. Packham and his team moved on to longer wavelengths to get a better picture of the entire torus. Combining observations across many wavelengths gives us a better sense of everything going on. Imagine only being able to see things that are blue, but having to figure out everything in a room. If you could also see red, yellow, and purple, you would get a much better idea what all is in the room. As promised, observations with SOFIA and ALMA further confirmed the clumpy model while better defining the structure of the torus.
Now, what does the future hold for AGN and the torus? Dr. Packham tells us there is still much to learn. The science team is currently working on a new MIR camera called MICHI, and when MICHI and JWST (launching October 2021!) observations are combined in the future, we will gain higher resolution images and spectra, be able to trace thermal disk emission to potentially probe forming planets, probe snow lines, and even detect complex organic molecules.
Live-tweeting of the session by Briley Lewis
Special Session: Astronomy and Satellite Constellations (by Briley Lewis)Conversations in astronomy about protecting the night sky from light pollution have been going on for decades, but satellite constellations and the rapid industrialization of space have brought about new challenges. There are cultural, environmental, health, and scientific impacts to be considered, but as panelist Jeff Hall (Lowell Observatory) said today, space is currently a bit of a “Wild West environment.”
To address these challenges and inform policy decisions, astronomers and satellite operators have collaborated to mitigate the effects of these satellite constellations. In the past few years, the NSF and AAS hosted the SATCON1 workshop, culminating in a report on impacts and mitigation strategies, and the IAU and partners hosted the Dark and Quiet Skies workshop, creating a report to be presented to the UN Committee on the Peaceful Use of Outer Space. The AAS also maintains a Committee on Light Pollution, Radio Interference, and Space Debris. In today’s session, astronomers and satellite operators met once again to discuss these issues and increase awareness of these issues with AAS members.
When SpaceX’s Starlink satellites first went up, many people panicked upon seeing images of the night sky filled with bright streaks. Panelist Patrick Seitzer (University of Michigan, Ann Arbor) reported that the AAS has set a goal for these satellites to stay at magnitude 7 or fainter; that is, they shouldn’t be visible to the naked eye in excellent dark sky conditions. There’s a caveat to this though: objects further away may look fainter to our human eyes, but an object in a higher orbit is actually in better focus for a telescope and has a longer travel time (thus, exposure time) across a detector, causing more problems for astronomy. As a result, the AAS additionally recommends that these satellites stay below 600 km.Panelist Harvey Liszt (NRAO—Charlottesville) then went on to describe the effects of these satellite constellations on radio astronomy. Certain bands are designated as protected for radio astronomy, but satellites often infringe on the edges of these bands or exploit complexities in FCC rules to engage in behavior that is harmful to radio astronomy. One participant pointed out that radio astronomy is also done outside of these protected bands, so avoiding those regions alone doesn’t mean a project has zero impact. Aparna Venkatesan (University of San Francisco) brought yet another dimension to this discussion, reminding us that the night sky and other resources “have value outside of their utility and what we do with them.” She asked participants in this discussion to consider who is missing from our decision-making, and to consider that there are other value systems and cultural perspectives to bring to these issues, reminding us that BIPOC are already dealing with a crisis from the disproportionate effects on them from climate change, the COVID-19 pandemic, systemic racism, and more. (You can read more from Venkatesan on space as an ancestral global commons here.) She also pointed out that pace is an issue, since everyone is trying to get this done first; the industry of satellite constellations is very fast paced, which means it’s also capable of responding quickly — but it often does not mesh well with the slow, ponderous, Ent-like pace of academic science.Next, each satellite operator gave an overview/update on their mitigation efforts. Patricia Cooper, representing SpaceX’s Starlink, stated a goal of having their satellites be invisible to the naked eye within a week of launch. They are minimizing their impact by adding sunshades to block antenna reflection and maneuvering satellites to reduce their reflective surface area. Julie Zoller, representing Amazon Kuiper, states that although they have not yet launched any satellites, they are using astronomers’ recommendations in their designs. They are using the minimum number of satellites needed to provide service, staying below the recommended altitude, and using steering that allows them to roll and minimize reflection similar to Starlink. Zoller also expressed the importance of their service, stating the need for reliable internet in underserved communities, which is a problem that has only been worsened by the pandemic. Lastly, M. Vanotti, representing OneWeb, started off by saying their company is recovering after filing Chapter 11 bankruptcy. They have also recently reduced the number of satellites in their constellation and say they are committed to responsible space operations, but their orbiting altitude is still set as 1,200 km, far above the recommended orbits. All three companies present also confirmed that they have plans for de-orbiting their satellites at the end of their operational lifetimes. Amazon Kuiper, due to their low orbits, will be able to de-orbit within one year with propulsion systems, or within ten years if propulsion fails.
Responding to questions about international coordination of mitigation efforts, panelists suggested that the orbital debris tracking community could be a good example to look to. As Jeff Hale aptly said, “Lots of people are trying to get into the game, and bad things will happen if they just don’t care.” Hopefully, the satellite operators will continue to consider astronomy and other impacts in their plans, and these conversations between stakeholders will continue as well.
Press Conference: Evolving Stars & Nebulae I (by Ellis Avallone)The second press conference of the day was all about evolving stars and nebulae, and the talks centered primarily on eclipsing binaries and supernova remnants. James Davenport from the University of Washington started off by discussing the exciting eclipsing binary HS Hydrae. Although HS Hydrae was first discovered in the 1960s, recent observations have allowed us to understand some of the strange behavior it exhibits. The amplitude of the eclipse signals in this system’s light curve has been gradually decreasing since its discovery, and this is due to a third non-eclipsing star that causes the two inner stars to “tumble” through space. It was predicted by astronomers in 2012 that sometime in 2022, the eclipses of HS Hydrae would vanish entirely. Last year, TESS observed this star just before this critical point. Davenport and his team were then interested in whether this variability persisted prior to HS Hydrae’s initial discovery. They consulted the DASCH project, which catalogues photographic plate data from as far back as the 1880s. This archival data showed that this change in HS Hydrae’s eclipse amplitude had been seen before, and confirmed that we should expect to observe eclipses again in about 200 years. Press release
Next, Ethan Kruse from NASA Goddard SFC told us about how we can use machine learning to discover eclipsing binaries in survey data. We have the best chance of detecting lots of eclipsing binaries when we look at the sky for a long time, i.e., with survey telescopes. While Kepler helped us out a ton with getting binary light curves with long baselines, it only looked at a small patch of the sky. The TESS mission, Kepler’s younger sibling, is an all-sky survey that can give us an orders-of-magnitude larger sample than Kepler. The machine learning pipeline developed by Kruse and his team has already detected 20,000 eclipsing binaries in TESS data within their small test sample. As the TESS mission continues, we expect to add tens of thousands of these interesting systems to our current sample.Moving on, Sagiv Shiber from Louisiana State University discussed an interesting aspect of binary star evolution. The phenomenon, called grazing envelope evolution, occurs when the envelope from an evolved primary star grazes the orbit of a less-evolved companion. Grazing envelope evolution sets on when jets erupt from an accretion disk around the companion. Shiber determined that these jets prevent the companion star from being engulfed by the evolved primary and that jets can cause fast outflows from the poles of the system, which leads to the presence of lobes in the stellar remnant. Press release
The last two talks were all about supernova remnants. First, Dan Patnaude (Center for Astrophysics | Harvard & Smithsonian) talked about the connection between supernova remnants and the supernovae that formed them. Although we have very few examples where we’ve observed both supernova and remnant, a recent detection caught the eye of Patnaude and his team. SN1996cr is located in the nearby Circinus galaxy, and although the initial supernova wasn’t observed in detail, archival data has assisted tremendously in characterizing this object. Patnaude has been able to effectively look back in time with this object, even without perfect observations.Finally, John Banovetz from Purdue University discussed the characterization of another supernova remnant, 1E 0102.2-7219 (also known as E0102). Using archival images from Hubble, Banovetz determined the location of the expansion center by considering the trajectory of the expanding material. The difference between the expansion center and the location of a possible surviving neutron star indicate a high velocity of the remnant. Banovetz was also able to determine that the system is about 1,700 years old. Press release
Live-tweeting of the briefing by Ellis Avallone
Dannie Heineman Prize for Astrophysics: The All-Sky Automated Survey for Supernovae (by Mike Foley)
The final plenary talk of the day was given by Chrisopher Kochanek (The Ohio State Univ.), this year’s recipient of the Dannie Heineman Prize, an award that recognizes outstanding mid-career work in the field of astrophysics. Dr. Kochanek is one of the architects of ASAS-SN, the All-Sky Automated Survey for Supernovae. ASAS-SN is fully automated and can observe and identify transient objects without human intervention. A transient object is anything that changes substantially in the sky over time; asteroids, cataclysmic variables, novae, and supernovae are the most common. By taking a large number of images across the sky and comparing images of the same region over time, ASAS-SN can identify what changes between images.
To do this, ASAS-SN doesn’t need large telescopes. In fact, their network of telescopes features individual mounts that have four lenses, each only 14 cm in diameter. By distributing these mounts around the world and continually monitoring the sky, ASAS-SN aims to serve as the “first responder” when a transient event occurs. Once ASAS-SN reports on a transient event, it can be followed up by larger telescopes for further study. Dr. Kochanek noted that amateur astronomers also play a large role in detecting and following up on transient events! ASAS-SN has historically done better at detecting supernovae closer to the centers of their host galaxies (the galaxy in which the supernova went off) than both amateur and professional surveys.ASAS-SN has been incredible for detecting huge quantities of variable events that other surveys often miss. For example, ASAS-SN has identified over 400,000 variable stars, with over 200,000 of those representing new discoveries. Thanks to its continuous monitoring of the sky, it also has observed a number of particularly interesting objects. These include repeated partial tidal disruption event ASASSN-14ko and an extreme version of a heartbeat star, where the emitted light goes through quick periods of dimming and brightening that resemble a human heartbeat.
Finally, ASAS-SN also provides a remarkable amount of data for static sources, such as normal stars. Later this year, Dr. Kochanek and collaborators will release Sky Patrol 2.0, which will feature continuously updated light curves for 106 million stars! ASAS-SN has been one of the leaders in promoting open data, creating a full database for users to query light curves observed by ASAS-SN. Thanks to Dr. Kochanek and the ASAS-SN team, the night sky is being well-monitored.