AAS 241: Day 4

Editor’s Note: This week we’re at the 241st AAS meeting in Seattle, WA, and online. 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 for daily summaries, or follow @astrobites on Twitter for live coverage. The usual posting schedule for AAS Nova will resume on January 18th.

Table of Contents:

Plenary Lecture: John Mather (NASA Goddard Space Flight Center) (by Briley Lewis)

John Mather’s plenary was a celebration. He opened by thanking the 8 billion humans on Earth, 10,000 observers, 20,000 engineers, and 100 scientists worldwide for making the huge endeavor of JWST happen, and then took the audience on a whirlwind tour of JWST’s history and the highlights of its first year of discovery. From tracing dark matter to revealing the earliest galaxies, taking photos of planet-forming disks to peering into Titan’s hazy atmosphere, watching an asteroid attack to puzzling over shells around a star, it’s truly been a year of great scientific progress and a whole lot of gorgeous images, too.

Mather also looked towards the future, with shout-outs to so many exciting ongoing projects: Euclid, NGRST, the Vera Rubin Observatory/LSST, thirty-meter class telescopes (TMT, eELT, and GMT), and the Decadal-recommended Habitable Worlds Observatory (also sometimes known as LUVEx, a portmanteau of the telescopes that inspired it — LUVOIR and HabEx). He even speculated beyond that, sharing future concepts like hybrid ground-and-space-based observatories using artificial satellites as orbiting guide stars for adaptive optics systems or as stations for very-long-baseline interferometry (VLBI).

The big takeaway here is that we’ve done some incredible things as a community, and we have so much more to come. “Celebrate, and then write proposals!” he told the astronomers in the audience. “We’re just getting started.”

Live tweets of this session by Briley Lewis.

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Press Conference: Clouds and Nebulae (by Pratik Gandhi)

One of the final press conferences of the 241st AAS was focused on clouds and nebulae, and by extension supernovae and other processes that lead to the formation of clouds and nebulae.

Dr. Gerrit Verschuur and Dr. Joan Schmelz were first up, showing new results on distance measurements to the high-velocity cloud (HVC) complex M. This year marks the 60th anniversary of the discovery of this HVC in the Milky Way, and its velocity is much higher than the rotational velocity of the galaxy. Their team made the first-ever distance estimate for any HVC, and they found that there is a stream of gas between the star MI and the gas filament (which is now called Complex M). Radio data also shows that there is a large cavity associated with the complex, which appears to be the result of a supernova that exploded 4 million years ago! The team also inferred a distance of 307 parsecs and a total supernova energy output of 3.5 x 1050 erg. Finally, they concluded by mentioning that the “Local Chimney,” a low-density extension of the well-known “Local Bubble,” likely came from this progenitor supernova.

Next, Dr. Robert Fesen talked about the exceptional supernova remnant Pa 30. This remnant is really interesting because it was discovered in 2013 by amateur astronomer D. Patchick using data from the WISE mission. In recent years, different teams from Hong Kong, France, and Russia discovered a really unusual massive white dwarf star at the center of the remnant, with some astounding properties like really high-velocity winds and high luminosity. This star could be the product of the merger of two white dwarfs, resulting in a rare Type Iax supernova. The other really fascinating thing about this supernova is that it likely happened only a thousand years ago, which is really recent on galactic timescales!

Dr. Bruce Balick continued the press conference with a talk on “The tempestuous life of the Butterfly Nebula, NGC 6302.” Although his take on it was that it “doesn’t look like much of a butterfly, but rather a dragon sneezing fire all around it.” This nebula is an example of an unexpected stellar evolution result. While most planetary nebulae are symmetrical and formed gently (not from explosions), the Butterfly Nebula is asymmetric, much bigger, and a lot more chaotic. Their team compared Hubble Space Telescope images from 2009 and 2020 and found that there appear to be multiple outflows of gas and other material from the central regions, with different outflows having different directions and different ages. Dr. Balick concluded by saying that observations of the Butterfly Nebula are compatible with a rare triple-star accretion disk model, while single and binary star models are too simplistic to be applicable and do not explain all the observed features.

The final presentation was by Dr. Peter Barnes, who talked about “the case of the masquerading monster in BYF 73.” Cloud BYF 73 is a massive cloud about 8,000 light-years away, with an associated nebula. The mystery associated with it is an inflow of material towards the center, which happens to be the highest rate of mass inflow towards a protostellar object ever seen! Their team used observations from the SOFIA and ALMA observatories, and found strong polarization of magnetic fields in the nebula, and weak polarization in the protostellar core. They also found that the gas infall towards the center is faster than expected, implying a 4–6 times larger protostellar mass than thought, of about 1,000 solar masses. Thus the central protostellar object has been labeled a “masquerading monster”!

Live tweets of this session by Pratik Gandhi.

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Plenary Lecture: Sangeeta Malhotra (NASA Goddard Space Flight Center) (by Isabella Trieweiler)

Dr. Sangeeta Malhotra kicked off her plenary talk, “Tiny Mighty Galaxies,” by promising many vegetable puns and a little bit of science. Dr. Malhotra is a researcher at the NASA Goddard Space Flight Center and works on low mass galaxies. She grew up in Delhi, earned her PhD in Astrophysics from Princeton University (becoming the first woman of color to do so!), and was part of the inaugural class of American Astronomical Society fellows. She was previously a professor at Arizona State University and moved to Goddard to work on the Nancy Grace Roman Telescope (formerly WFIRST).

Dr. Malhotra’s research focuses on Lyman-alpha (Lya) galaxies. The Lyman-alpha line is a spectral line of hydrogen; Lya photons are created when electrons fall from the second energy level down to the ground state. Any star-forming galaxy can make Lya photons, so Lya galaxies are just the particular cases where Lya photons are able to escape the galaxy and be observed. Figuring out exactly what allows Lya to escape some galaxies but not others is an open question. Dr. Malhotra showed that Lya galaxies have some common characteristics — they tend to be small in size, with low metallicity and low dust content. Additionally, many Lya galaxies are young, with low stellar masses but high gas pressure and strong emission lines, hence the label “Tiny Mighty Galaxies.”

Lya galaxies are cosmologically important because they help us understand the process of reionization by providing constraints on the amount of neutral hydrogen present at a given time. Connecting the galaxies with reionization requires a really good understanding of the physics of Lya escape, and that’s where the vegetables come in! Over the course of Galaxy Zoo, a citizen science project tasked to identify and categorize galaxies, members of the public helped find a new kind of galaxy, affectionately named “Green Peas.” Green Pea galaxies are small, round, and green in color, hence the name. They have very strong emission lines, particularly ones produced by oxygen. They also happen to be a very good local universe counterpart to the high-redshift Lya galaxies used for reionization studies. Dr. Malhotra’s group uses Green Peas to test their models of Lya escape and have found that factors such as dust content and peak velocities are some of the best determinants of Lya escape.

The other component needed to connect Lya galaxies and reionization is a large sample of Lya galaxies at high redshift. Dr. Malhotra is working on this via the LAGER survey, which aims to find Lya galaxies at a redshift of 7. The survey is an international collaboration and uses a narrow band approach to identify the bright Lya lines in galaxies. Dr. Malhotra’s involvement in the Roman telescope will also be crucial to reionization research as the telescope’s extremely wide field of view will help astronomers understand how reionization occurs on scales spanning many clusters of galaxies.

slide from Sangeeta Malhotra's plenary talk

[Slide by Sangeeta Malhotra]

Finally, Dr. Malhotra closed her talk by urging senior scientists to put effort into the retention of students of marginalized identities. She presented a summary of her own previous mentees and showed that the majority of women and students of color have since left the field. She reminded students to prioritize their own mental and physical health, and to ask for help as needed, but stressed that the responsibility for the problem is absolutely on senior faculty. She called on mentors to take notice of any similar trends amongst their own students and to get to work solving this issue in astronomy.

Live tweets of this session by Isabella Trierweiler.

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Press Conference: Signals from Neutron Stars and Black Holes (by Graham Doskoch)

The final press conference of AAS241 focused on compact objects: black holes and neutron stars. Four speakers took the podium, presenting discoveries of several new types of astronomical objects — and a couple of old favorites. First up was Prof. Eric Coughlin of Syracuse University. Prof. Coughlin and collaborators studied a tidal disruption event, or TDE, called AT2018fyk. TDEs occur when a supermassive black hole tears apart a nearby star, feasting on its gas and emitting a high-energy outburst. These are usually cataclysmic events, but the group noticed that 600 days after the outburst, AT2018fyk dimmed — and then experienced another, similar outburst 600 days later.

This isn’t supposed to happen with TDEs! The group proposed a model to explain this repetition: a partially disrupted TDE. A star near the supermassive black hole was tidally disrupted, but only partially; some of its gaseous envelope was accreted, leaving a partially-stripped remnant that kept circling the black hole on a 1,200-day orbit. One orbit later, it was once again disrupted. The model predicts that there should be another event this coming August. Will it happen? We’ll have to wait and see.

The next speaker was Emily Engelthaler, of the Center for Astrophysics | Harvard & Smithsonian. She had performed ultraviolet spectroscopy of another TDE (this time not a repeater!). The emission showed a number of expected features, including carbon lines, showing the fast-moving material in the black hole’s accretion disk. What was interesting was the amount of variability, and the eventual disappearance of this carbon emission. Engelthaler proposed that the “puffy doughnut” of material is getting less “puffy,” leading to changes in the spectral absorption and emission.

Engelthaler was followed by Rose Xu, an undergraduate at Bard College. Xu presented results on X-ray flares from Sagittarius A*, the supermassive black hole at the center of the Milky Way. While Sgr A* isn’t as active as many others of its kind, it does exhibit X-ray and infrared flares on a roughly daily basis. Xu was interested in addressing an unresolved question: What’s the mechanism behind these flares? She and her collaborators searched data from the NuSTAR X-ray telescope, discovering seven new flares from 2016 to 2022, including a double-peaked flare. The ground found tentative evidence that bright flares and faint flares may have spectral differences, a hint that they could be caused by different processes.

The final speaker, Dr. Amruta Jaodand of Caltech, presented new results on an unusual pulsar, J1023+0038. Pulsars are the dense, rapidly rotating remains of massive stars, and they emit beams of electromagnetic waves, which sweep across our line of sight, like a lighthouse. This appears as periodic emission, usually at radio wavelengths but occasionally in X-rays and the optical. A subclass of pulsars, millisecond pulsars, spin several hundreds of times per second, after accreting material — and angular momentum — from a companion.

J1023+0038 is a type of millisecond pulsar called a transitional millisecond pulsar. It’s in the process of this accretion, and switches between different modes, one involving X-ray emission and one involving radio emission. Jaodand found that the pulsar also emits ultraviolet pulses; while it’s not the first known UV pulsar, it is the first known UV millisecond pulsar. Coupled with its strange X-ray and radio behavior, this may give insight into pulsar emission mechanisms.

Live tweets of this session by Graham Doskoch.

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Plenary Lecture: Dan Foreman-Mackey (Flatiron Institute) (by Mark Popinchalk)

When Dr. Dan Foreman-Mackey showed a functioning code block on one of his first slides, he whimsically remarked “I don’t think any other plenary has put Python code in their talk,” which was met with a round of laughter. And it’s probably because no other plenary was trying to do what Foreman-Mackey did — spend 40 minutes presenting the motivations, grand ideas, and power of the open source software he’s worked on in his career.

The scientific example that was used was using Gaussian processes to fit a Kepler light curve showing a transiting planet. But that quickly became a background feature to the three Gaussian-process libraries that Foreman-Mackey had created at different stages in his career; george, celerite, and tinygp.

With his natural charm he carefully laid out the major improvements that each of the three packages incorporated into the computation of Gaussian processes. george made a step away from rote implementation, instead offering a library of kernels (tools used to construct the Gaussian-process model). celerite (“Imagine there are accents if you want to pronounce it properly [i.e., celerité]”) used linear algebra to speed up the Gaussian-process calculation, and tinygp used JAX at its core to speed it up even further.

But it wasn’t the technical achievements that were the most impressive. It was the intention behind the packages that truly shined the brightest throughout the plenary. Foreman-Mackey is a champion of open-source software, where the codebase is public, documented, and easily accessible. Some might cringe at the thought of all their work laid bare for anyone to scrutinize. However, it was clear that Foreman-Mackey thought this was a strength. That a code was made for others meant that it needed to be flexible, that public eyes would find the room for improvements and innovations, that there is a strength in trusting the community of your peers.

This wasn’t a plenary on a topic so much as it was a plenary on a way of working. Littered with little jokes, personal anecdotes, and even more lines of code, the talk wasn’t about empowering the audience with knowledge, but encouraging them to try new code and ultimately experience the ecosystem of open-source coding of which Foreman-Mackey is a clear and vocal champion.

Full slide deck: https://speakerdeck.com/dfm/open-software-for-astrophysics-aas241
Live tweets of this session by Mark Popinchalk.

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Berkeley Prize Lecture: Anthony Brown (Leiden University) (by Ali Crisp)

Dr. Anthony Brown gave his plenary on the Gaia mission, for which he and his team were being awarded the AAS Berkeley Prize. He began with an overview of the mission, including a joking remark thanking the JWST team for putting their telescope at L2 (where Gaia is also located) so he doesn’t have to explain what that means in his talks anymore. He emphasized the teamwork aspect of the Gaia mission, listing all the different teams in the Gaia Data Processing and Analysis Consortium (Gaia DPAC) and their contributions to the project.

A group picture of the Gaia collaboration

A group picture of the Gaia collaboration. [Slide by Anthony Brown]

Dr. Brown then gave an overview of the data Gaia has collected so far and all the different astrophysical parameters it gathers. To date, Gaia has measured fundamental parameters such as stellar radii and temperature for over 471 million stars. Of those 471 million stars, there are also 2.5 million stars with detailed chemical abundance measurements, 1 million stars with high-resolution spectra, and 219 million star with low-resolution spectra. 800,000 binary systems have also been cataloged in the mission!

Dr. Brown continued by highlighting Gaia science contributions, starting with providing astrometric measurements of Arrokoth to the New Horizons team, so they could make accurate orbital calculations for the spacecraft’s approach. Gaia data were also used to calculate the precise luminosity functions required to confirm that carbon–oxygen white dwarfs undergo crystallization in their interiors. Gaia’s precise astrometry has also been used to confirm the existence of a black hole, to make 3D maps of nebulae such as Orion, and to build clearer pictures of how different elements are distributed in the Milky Way, which in turn give us a better idea of the galaxy’s formation history.

Dr. Brown ended his talk by listing what new data products will be included in the fourth and fifth Gaia data releases, including updated astrometry, time-series data, and much, much more. He kindly requests that — should you use Gaia data for your research — you give the team credit for their hard work. Specific information on how to acknowledge Gaia can be found here.

Live tweets of this session by Ali Crisp.

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