Astrobites at AAS 243: Day 4

The galaxy contains delicate filaments of gas and dust in the grandiose spiral arms which wind outwards from the center of this image. A lack of gas in the nuclear region also provides an unobscured view of the nuclear star cluster at the galaxy's center.
JWST image of the galaxy NGC 628. (Credit: ESA/Webb, NASA & CSA, J. Lee and the PHANGS-JWST Team; Acknowledgement: J. Schmidt; CC BY 4.0)

Welcome to the winter American Astronomical Society (AAS) meeting in New Orleans, LA! Astrobites is attending the conference as usual, and we will report highlights from each day here. You can also follow us on BlueSky at astrobites.bsky.social for more meeting content. We’ll be posting once a day during the meeting, so be sure to visit the site often to catch all the news!

Table of Contents:


Committee on Astronomy and Public Policy Plenary Lecture: Lia Epperson (American University – Washington College of Law) (by Briley Lewis)

The final day of AAS 243 began with a plenary on an important topic: what the recent Supreme Court decisions on the use of race in college admissions mean for us as educators. In these cases, a group called Students for Fair Admissions (SFFA) challenged Harvard University and University of North Carolina (UNC) on their race-based considerations in admissions.

Epperson began by saying, “In an era where sometimes the pursuit of knowledge is maybe less appreciated than we would have liked as educators, I think it’s important for all of us to really understand the history of how we got to this moment.” Before diving into the details of the current cases, she provided an overview of how race, education, and affirmative action have been intertwined in the history of US law.

Race is embedded in the US Constitution (with the three-fifths, importation, and fugitive slave clauses), clearly indicating that our country’s founding document cared about “embedding a racial hierarchy,” said Epperson. This initial founding law has had “ripple effects on education and access to education” throughout US history, she added.

The first landmark case on education and race was Sweatt vs. Painter in 1950, when a Black student challenged a Texas law school. The Supreme Court decided that denying admission denied the student “standing in the community, traditions, and prestige customarily accorded to white students.” This ruling made clear that diversity and inclusion were to be considered a fundamental part of higher education.

Soon after, in 1954, the famous Brown vs. Board of Education ruling was issued, establishing separate education as inherently unequal. The term “affirmative action” then appeared in 1961 — not as a Supreme Court ruling or law specific to education, but from an executive order from President Kennedy initially intended for employment and contracting. The order stated that “government contractors may take affirmative action” to ensure treatment is not racially divided.

Forty years of legal precedent thereafter solidified the importance of race in holistic admissions processes, citing the benefits to democracy and pathways to leadership provided by education. Three crucial cases in this precedent were Bakke vs. Regents of UC Davis (1978), Grutter v. Bollinger and Gratz v. Bollinger (2003), and Fisher v. Texas I and II (2003, 2006). Research on K-12 schools has also shown that diverse schools improve students’ critical thinking skills, increase their civic engagement, and lead to higher graduation rates.

The Harvard case was the first to challenge race-conscious admissions, at an institution that excluded people of color for 85% of its 400-year history. UNC was founded in 1789 to serve the children of slave owners and didn’t admit their first Black student until 1951 (and even then, it was only due to a federal court order).

The questions posed before the court in these two contemporary cases were the following: Does Harvard violate Title IX by discriminating against Asian Americans? Do these schools fail to use race-neutral alternatives? Do they use race as more than just a factor to boost applicants?

Lower court decisions upheld the precedent supporting race-conscious admissions, yet the Supreme Court changed tack. In a decision that Judge Ketanji Brown Jackson described as defying “law, history, logic, and justice,” the court cited that there was no compelling interest to continue affirmative action (considering diversity only a “commendable goal”), claimed that affirmative action relied on racial stereotypes, and that there was no clear end in time for affirmative action as described in the past.

Epperson clearly described what colleges may and may not do in the wake of this decision, and factors the court did not address. Colleges may design their missions as they see fit, and they may include qualities from student experiences based on race. The decision did not address scholarships, financial aid, recruitment, retention, pathway programs, employment, or DEIA programs — only admissions. It also does not affect employment, which is covered by Title VII of the Civil Rights Act.

Additionally, colleges are still allowed other forms of affirmative action that universities use to shape their student population. Legacy admissions are still legal, and often biased towards white students; for example, Princeton legacy applicants have nearly a 30% success rate in admissions, while everyone else has a less than 5% shot. Similarly, colleges are allowed to consider major donors, demographic/regional preferences, socioeconomic status, and athletes. Shockingly, only 11% of athletes would be admitted without this bonus factor in their favor. 

In the wake of this decision, SFFA is instigating further litigation, including a challenge to a prestigious high school magnet program focused on diversity, to fellowship and grant programs aimed at increasing diversity, and to West Point (because the original court decision didn’t apply to military academies). Epperson also highlighted ongoing efforts to counter these efforts and increase diversity in university admissions: targeted recruitment and retention, a more holistic admissions process, elimination of other forms of affirmative action (e.g., legacy), elimination of college entrance exam requirements, and legislation to further diversity. 

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Press Conference: High-Energy Universe (by Mark Popinchalk)

It’s the last day of AAS, and while attendees might have low energy, this press conference was full of high-energy (astrophysics)!

Evidence of a Relic Active Galactic Nucleus Eruption

The press conference started with Kimberly Weaver (NASA Goddard SFC) telling us how XMM Newton found a relic of an eruption from an active galaxy! Active galactic nuclei (AGN) are the centers of galaxies with a supermassive black hole accreting a hot disk of material. This produces lots of energy, and it can even produce high-powered jets, such as the AGN in Messier 87.

The team wanted to understand how AGN may affect star formation and power galactic outflows. All this high energy and moving matter should have a significant effect on galaxy evolution, and it was expected that one could trace previous nuclear activity. 

So the researchers used ESA’s XMM Newton to look at NGC 4945. NGC 4945 is a spiral galaxy, also classified as a starburst due to its recent star formation. XMM has high sensitivity and a wide field of view. With just one observation they could image the entire galaxy.Using their data, they saw that high-energy X-rays were outlining a huge clump of cold gas, 32,000 light-years long! But there were clearly some things in the way of the gas, such as individual stars and the light from the AGN itself. So they took further images using NASA’s Chandra X-ray Observatory. Using these observations they could remove the intervening features and still see a huge amount of cold gas.

A slide from the press conference of Kimberly Weaver showing cold gas in a distant galaxy
A slide from the press conference of Kimberly Weaver showing cold gas in a distant galaxy

The gas lined up with other observations suggesting a strong collimated outflow of material. The team thinks that 5 million years ago, jets from the AGN weren’t aimed out into space like they are in Messier 87, but instead smashed into the rest of the galaxy! Theory says that once they smash into the thing, the jets then disappear. So what we have leftover is a relic signature of how the jet drove in and left behind the cold gas clouds as a fossil of that activity.

Unveiling the Most Promising Formation Channel of Fast Radio Bursts Using Local Universe Bursts

Next up were Aaron Pearlman (McGill University) and Mohit Bhardwaj (Carnegie Mellon University), who were presenting the evidence for a potential dominant formation channel of fast radio bursts (FRBs). FRBs are bright radio pulses of millisecond duration. What causes them is unknown, but the source must be very powerful, as the signals travel between galaxies. We know this because as radio waves move through intervening material, the signal disperses, and the amount of dispersion in FRB signals implies that they come from outside the galaxy.

But what causes them? And can there be multiple formation channels? The researchers used the CHIME radio telescope. Using it, they are able to find roughly 100 new FRB per month. Using the telescope they can identify the location of the FRBs within 1 arcmin. 

Using their previous database, they associated four of the FRBs to nearby spiral galaxies. Then they looked at other local universe FRB sources that were associated with a galaxy, and saw that the sources are spiral galaxies.

Now that they had spiral galaxies as a clue, they could rule out many of the proposed formation methods. Globular clusters as a source was out, as we would see them from elliptical galaxies too. Certain stellar interactions? No way, otherwise it wouldn’t just be spirals either. Since they were all coming from spirals, they think this means it has to be one thing and one thing only: core collapse supernovae.

A slide from the press conference of Aaron Pearlman and Mohit Bhardwaj showing potential origins of fast radio bursts

The prevalence of spiral hosts in the local universe is a major clue for FRBs, but it doesn’t answer everything. For example, we know of repeating FRBs — how does a supernova happen twice!

Evidence for Large-Scale Anisotropy in the Gamma-ray Sky

Next up was Alexander Kashlinsky (NASA Goddard SFC), who had a real mystery to share with us all, about the distribution of gamma-ray radiation in the universe. 

To start, there is a well-documented and studied dipole distribution in the cosmic microwave background radiation. In other words, there seems to be a preferred direction to it. There shouldn’t really be, but one possible explanation is that it could be due to the motion of the solar system making it appear that way.

If the CMD dipole is simply due to the solar system’s motion, then it should be detectable in gamma-ray radiation, too. If it isn’t, then it could have a potential cosmological implication.

Kashlinsky intended to probe for the dipole moment of the gamma-ray sky using Fermi LAT observations. Gamma rays are not microwaves, and due to relativistic effects they expected any dipole to be a bit higher in amplitude than that of the CMB.

However, what they measured was a gamma-ray dipole 10 times greater in amplitude than the CMB! They checked to see if the same is true for ultra-high-energy cosmic rays and found a similar dipole. They thought that maybe the ultra-high-energy cosmic rays are causing the gamma-ray dipole when they cascade and decay, but after looking at how that energy would be dissipated, it doesn’t make sense.

A slide from the press conference of Alexander Kashlinsky showing the location of the bizarre gamma-ray dipole

Instead, it may be possible that the ultra-high-energy cosmic rays and the gamma rays come from the same source. So this co-emission of both ultra-high-energy cosmic rays and gamma rays seems to be coming from a yet unknown source!

Astronomers Find Spark of Star Birth Across Billions of Years

Finally, Michael Calzadilla (MIT) asked the room how we arrived at the galaxies that we see today. Galaxies that we see today are either elliptical, sometimes called “red and dead,” while others are star-forming spirals. How do galaxies acquire the gas needed for star formation? Gas comes in and out of galaxies, and when the thermodynamics is right, stars can form. This atmospheric cooling has been known for the last 2 billion years and shown to be important for modern galaxies, but what about the past?

Well, the past was different! The peak of cosmic star formation was in the past, as well as galaxy mergers and black hole accretion, all peaking in the last 7–11 billion years. The challenge has been to find distant clusters and get multiwavelength follow up to understand their star formation.

The team used a well studied SPT-Chandra sample, which consists of an unbiased sample of 95 galaxy clusters spanning 10 billion years in evolution and that already had multiwavelength follow up.

A screenshot of the press conference of Michael Calzadilla discussing the atmosphere needed for star formation in galaxies

They showed that the necessary thermodynamic conditions to trigger star formation that exist in the most recent 2 billion years are also needed back to 10 billion years ago too. So, it seems like making stars is still pretty similar! However, they found that the black hole feedback that regulates star formation in the current universe might not be doing the same thing in the past.

Perhaps a topic for a press conference at a future AAS!

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Plenary Lecture: New Views of Dust and Star Formation in Nearby Galaxies with JWST, Karin Sandstrom (University of California, San Diego) (by William Lamb)

JWST is the gift that keeps on giving. It’s revolutionising astrophysics, cosmology, and our view of the universe. In this plenary, Dr. Karin Sandstrom offered attendees a snapshot of the incredible science that is being conducted with JWST after only 1.5 years of science operation.

Before JWST, there were some outlying questions regarding the baryon cycle: the flow of gas and dust from the interstellar medium onto galaxies that fuels star formation, which then causes the expulsion of material via outflows from the galaxy back into the interstellar medium. Those questions include what controls the gas reservoir for star formation and what controls the efficiency of star formation?

Previously, we had limited techniques to trace the interstellar medium and stellar formation, but with the telescope’s resolution and sensitivity to the near- and mid-infrared spectrum, this is no longer an issue. For example, Dr. Sandstrom attempted to get the audience excited about polycyclic aromatic hydrocarbons (PAHs), which are large carbonaceous molecules. The infrared emission from PAHs is strongly correlated with the presence of the interstellar medium. Thus, this makes PAHs a high-resolution tracer, which means by detecting PAHs, you detect where the interstellar medium is and where it is flowing. JWST’s light filters were designed to capture the emission from PAHs, hence JWST can create high-resolution maps of the interstellar medium in our Local Group. With this new map, we can compare simulations of galaxy formation to high-quality data to improve our models, and further refine our models of stellar formation.

And of course, Dr. Sandstrom just had to share some of the stunning images from JWST’s remarkable instrumentation…

Dr. Sandstrom standing on a stage in front of a photo of a galaxy.
Dr. Sandstrom presenting an image of NGC 628 as taken by JWST.

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Press Conference: Oddities in the Sky (by Isabella Trierweiler)

True to its name, this session included a variety of puzzling phenomena that challenge our current astronomical models!

A Big Ring on the Sky

Alexia Lopez (Jeremiah Horrocks Institute – University of Central Lancashire)

The standard model describes our best understanding of cosmology in our universe, and it hinges on a critical assumption, that the structure of our universe is isotropic and homogeneous on the largest scales. Verifying the assumption of homogeneity is really important; we currently estimate that the scale of homogeneity is about 1.2 billion light years. In other words the universe should not have any overarching structures that are larger than this scale. However, two years ago Alexia presented one large scale structure that challenges homogeneity (the “Giant Arc”), and today she presented a second such structure called the “Big Ring”. The two structures are 3.3 billion and 1.3 billion light years across, respectively.

To find these structures, Alexia uses the light from distant quasars to identify clumps of intervening matter. From the quasar mapping, she can construct a 3D map of intervening large scale structure, with locations based on the dimmed quasars and distances extrapolated from MgII absorption. Both of the identified structures are curiously about 9.2 billion light years away, and are quite close together on the sky. However it’s unclear if this is a sign of a larger trend in the distribution of large scale structures. If these structures are proof that our current standard model for cosmology is insufficient, some options for improving our model include invoking cosmic strings, which may construct large scale structures, or assuming a “conformal cyclic cosmology” in which we are living in an infinite cycle of universes, resulting in the creation of circular structures. Alexia plans to continue her quasar analysis to get a better idea of how common these homogeneity-breaking structures might be. 

A Potentially Isolated Quiescent Dwarf Galaxy

Timothy Carleton (Arizona State University)

Timothy presented an odd galaxy that was fortuitously observed by the PEARLS project, an extragalactic survey using JWST. He noticed the galaxy (called PEARLSDG) in the PEARLS images due to its odd appearance relative to the other nearby galaxies, which were the original targets of the survey. PEARLSDG is a dwarf galaxy imaged in remarkable detail – JWST was actually able to resolve individual stars in the galaxy! While most dwarf galaxies imaged by PEARLS and other projects are either young and isolated or old with a massive companion, PEARLSDG sticks out as an old, isolated galaxy. How old and isolated galaxies form remains an open question, and Timothy says further spectroscopy of the galaxy will help characterize it and hopefully shed more light on how it formed. 

Timothy Carleton presents JWST observations of a potential isolated dwarf galaxy.
Timothy Carleton presents JWST observations of a potential isolated dwarf galaxy.

Close Encounters of the Supermassive Black Hole Kind: Tidal Disruption Events and What They Can Reveal About Black Holes and Stars in Distant Galaxies

Ananya Bandopadhyay (Syracuse University)

Supermassive black holes (SMBHs) are intriguing objects that are generally very difficult to study as they do not emit light. Because of this, tidal disruption events (TDEs) are especially valuable events, providing some insight into the properties of the SMBH. TDEs occur when a star approaches a SMBH and is disrupted by the strong tidal forces around the black hole. The disruption and accretion of the star in turn spark a flare whose lightcurve we can measure. TDEs are relatively rare, and we know of about a hundred of these events so far. The typical pattern for a TDE lightcurve is a rise in brightness over a 30-50 day period, followed by a gradual tapering off period. The main question in this work is what determines the peak luminosity and the timescale of this lightcurve. 

We typically use analytical approximations to recreate the shape of the lightcurves, but Ananya however demonstrated that the generally accepted analytical model for TDEs results in a very different light curve relative to detailed hydrodynamical simulations, motivating the need for a new model. She presented an updated model for TDE lightcurves in which she demonstrated that the timing of the peak in the lightcurve is actually independent of the mass of the accreted star, remaining at ~50 days across the board, while the peak luminosity of the TDE scales with the stellar mass. One of the implications of this finding is that TDEs that are energetic enough to cause jets around the SMBH are likely related to the disruptions of high mass stars. 

Impressively, much of the work of the project was completed by high school students! Syracuse University hosts a summer research program, and their student interns worked on the numerical simulations for the TDEs and are co-authors for this work. 

Zooniverse People-Powered Research Platform Reaches New Milestones

Laura Trouille (The Adler Planetarium; Zooniverse)

Zooniverse is the largest platform available for citizen science, with over 2.6 million participants around the world. It was started in 2007 through the founding of the GalaxyZoo project, in which members of the public helped classify different galaxy images. The platform grew rapidly, particularly after 2015 when a DIY project builder was added so that any researcher could easily create their own project. Laura shared that currently 40-50 new projects are added every year! Between the large user base and integrated machine learning algorithms, Zooniverse is a very powerful tool for analyzing large datasets and has led to over 400 scientific publications, often with citizen scientists included as co-authors. 

Laura noted a few recent results from Zooniverse projects. Having so many different eyes on the data makes Zooniverse especially good at identifying unusual features that would typically escape notice in simple coded pipelines. In the past few weeks, the project “Planet Hunters TESS” discovered a habitable zone planet while the “Backyard Worlds” team identified an aurora on a brown dwarf! To date, citizen science users have contributed 1.6 million hours of work to Zooniverse projects, the equivalent of nearly 800 full-time workers. 

If you’d like to contribute as a citizen scientist, getting involved is super easy! Consider joining the gamma ray bursts team, or hunt for asteroids with the Daily Minor Planet group. And if you’re a scientist who would like to start your own project, definitely do reach out to Laura and her team.

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Dannie Heineman Prize Lecture: Small Bodies: Primitive Witnesses to the Birth of a Habitable Solar System, Karen Meech (University of Hawaiʻi) (by Yoni Brande)

Professor Karen Meech, the winner of the 2023 Dannie Heineman Prize for Astrophysics, has spent her career studying small bodies (like comets and asteroids) in the Solar System. Her prize lecture today focused on how observations of these bodies can teach us about how both our own solar system evolved and how extrasolar planetary systems may be able to develop habitability.

Our current understanding of the development of life says that habitability needs liquid water, organic energy sources, and rocky planets. No currently-known extrasolar planetary systems meet these criteria, so we need to know whether the conditions in our Solar System are unique.

A common refrain in astrobiology is “follow the water”—that is, understand where water is in a system and how it moves around, and we should be able to predict where life might arise. In order to study the water content of the early Solar System, astrobiologists like Prof. Meech and her collaborators use remote observations as well as direct analysis of samples of comets and asteroids, which are cosmic detritus left over from those early eras. Prof. Meech showed a short review of this history, showing that within a few hundred million years of the Earth’s formation, it already had liquid water oceans. The main question, then, is how the water got here.

One theory says that icy bodies from the outer reaches of the Solar System were gravitationally scattered to the inner Solar System and eventually impacted Earth. This cometary water then became Earth’s main water reservoir. To test this, we can look at the ratio of deuterium to hydrogen. The D/H ratio of the early solar system is low near the Sun and increases with distance, making it a good tracer of formation location. Earth’s D/H value is significantly elevated for its current position, which is a point in favor of the icy body delivery theory. If high D/H comets swung by Earth and dropped off their water, that could increase Earth’s D/H. However, the last few decades of observations have shown mixed D/H results for different small bodies, and Prof. Meech stressed that we really don’t fully understand these primordial isotopic ratios, or if they are even meaningful in studying these formation and evolution processes. 

Ultimately, Prof. Meech says, water probably comes from multiple sources, we just need to figure out which sources and when. Planet formation is complex, with many chemical and dynamical processes jumbling up the possible tracers of this history. A newly observed kind of comet may finally untangle some of this historical web.

Long period, tailless comets called “Manxes” (named after the cat) show spectra similar to inner-Solar System rocky asteroids. Prof. Meech and her collaborators’ studies of manxes show they may have a complex history. They likely began their lives as normal main-belt asteroids (hence the similar spectra), but were dynamically scattered out to the Oort Cloud, and then scattered back into the inner Solar System on comet-like orbits. They appear to have a range of surface colors, which could be evidence of diverse formation locations across the Solar System. Prof. Meech concluded with some final thoughts: the study of Earth’s water is interdisciplinary, merging expertise from astronomy, planetary science, geology, and more. We need a better understanding of the chemical and dynamical history of our Solar System, and in order to do that we need in-situ explorations of Solar System planets, small bodies, and even interstellar interlopers like ‘Oumuamua. These topics have far-reaching implications for habitability and the origin of life. If the Solar System is not representative, and if the conditions here are special, we can’t assume all other potentially habitable systems will have them as well.

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Berkeley Prize Lecture: Wen-fai Fong (Northwestern University) (by Pratik Gandhi)

Prof. Wen-fai Fong, while receiving the Berkeley Prize, remarked that the award is important to her because it recognises not only her work but also that of her amazing research group. Throughout her plenary talk, she highlighted the work of her graduate students, postdocs, and external collaborators. Prof. Fong likes to study astronomical “transients”, or phenomena that are time-varying, using the technique of multi-messenger astronomy – probing these phenomena using observations across the entire EM spectrum from radio waves to gamma rays, and also gravitational waves. As she remarked, “the Universe varies on remarkably human timescales”, and she derives great joy from observing it in all its variety of colors. 

Speaking of colors, Prof. Fong highlighted three key themes throughout her talk: (1) Teamwork, which she discussed as being crucial for the kind of fast-paced, time-sensitive research required in transient astronomy, (2) the importance of color, in terms of leveraging the entire EM spectrum, and (3) that timing is everything, especially in the discipline that she and her group specialize in.

In terms of why the study of transients is important, Prof. Fong mentioned that they are often the birthplaces of numerous heavy elements, laboratories for studying extreme physics, the sources of gravitational waves, and probes of otherwise invisible material that we wouldn’t have noticed otherwise. The sources of transients are often the formation of the three classes of compact objects – white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). These compact objects are all the end stages of the life cycles of stars of different masses, with NSs and BHs occurring as a result of massive stars going supernova (which happen to be the most common transients).

Gamma-ray bursts (GRBs)

Prof. Fong mentioned how GRBs were first discovered in the 1960s, after which NASA developed multiple gamma-ray observatories in space. Thousands of GRBs have been detected to date, and they are usually extragalactic in origin. GRBs come in two populations (long and short), with short GRBs occurring during NS-NS mergers and long GRBs happening during the collapse of massive stars. Her group focuses mainly on short GRBs; the first evidence for which was the 2017 discovery of gravitational waves from a NS-NS merger followed by a GRB. Short GRBs have been detected in galaxies out to redshifts of z ~ 2!

Prof. Fong highlighted how when GRBs are detected (by the Swift telescope, for example), her phone will ping with notifications. Time is of the essence, because they have to mobilize multiple telescopes across the spectrum immediately. Right before Thanksgiving 2023 there was a GRB that was detected, and it was only through the amazing teamwork of her group that they were able to mobilize multiple telescopes and get memos (“circulars”) out to the transients community!

Questions that the Fong group is trying to address concerning GRBs include: what do two NSs create? How and where are heavy elements created? What conditions are required to produce these rare transients? The afterglow radiation that produces the GRBs gives us a handle on burst energetics. The NS-NS merger itself tells us about the mass of heavy elements produced. Finally, her group is working on building the BRIGHT repository, a catalog of galaxies that host GRBs, to try to understand the conditions required for them to occur.

Fast radio bursts (FRBs)

Prof. Fong also highlighted a second kind of transients, which have only recently been discovered. In 2007, a serendipitous discovery sparked the fast radio burst (FRB) revolution. FRBs are millisecond bright radio pulses similar to GRBs but on the radio side of the spectrum. Some FRBs repeat periodically while others do not, and the cause of this difference is still unknown! Leading hypotheses for the sources of FRBs include magnetars, or extremely magnetized neutron stars. The Fong Group is part of the “Fast and Fortunate FRB Follow-up” (F^4) collaboration, which mobilizes telescopes across the EM spectrum from ALMA to Chandra, in order to also look at the host galaxies of the FRBs.

Prof. Fong concluded the talk by returning to the importance of teamwork, color, and timing, and saying, “there is incredible momentum behind this field and the era of 1000+ hosts is not far away – we’re thrilled; we’re excited; we’re scared!”

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