Astrobites at AAS 236: Day 2

Welcome to the summer American Astronomical Society (AAS) meeting, held virtually for the first time! 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 #aas236 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! 

Composite image shows dust at the galactic center, with streamlines superposed to show the motion of plasma.
This composite image of the galactic center shows how magnetic fields (seen here as streamlines) govern the motion of plasma around our supermassive black hole. [NASA/SOFIA/L. Proudfit, ESA /Herschel/Hubble Space Telescope]

AAS Publishing Exclusive: A Discussion with the arXiv Executive Director (by Alex Pizzuto)

Day 2 of the meeting started strong, featuring a discussion with arXiv Executive Director Eleonora Presani, who detailed the current status and future outlook of the open access archive service many of us know and love. Not only is Presani new to the role of executive director, but the role itself is only two months old, marking a step towards engaging with the scientific community more efficiently and productively. As someone equipped with both a PhD in astroparticle physics and more than 6 years of experience from a career in scientific publishing, Presani is extremely qualified to help execute the vision of arXiv.

Presani began her presentation with her own mantra on the dissemination of scientific research: “knowledge only exists if it is accessible.” As an organization, Presani believes that arXiv functions as the “enablers” for the sharing of this knowledge, and seeks to make accessible environments like arXiv; those which are for researchers, by researchers. To get a sense of the sheer volume of knowledge that passes through the arXiv servers, Presani quizzed her audience, revealing some dumbfounding statistics about the quantity of preprints that have been submitted:

The fact that about half of the funding for arXiv is from the community is a testament to the fact that arXiv exists to serve the community. 

Although many organizations have been slowed to a halt by the tragic global pandemic, Presani assures us that arXiv is still working hard. Over the last few months, arXiv has rolled out user-driven classification, which alerts authors when they assign their papers to a category that disagrees with arXiv’s classification algorithm. They have also been executing operational stability drills and developing a COVID-19 moderation plan, to make sure that no matter what is going on in the world, scientists can stay connected through their research.

Looking more to the future, we were then told about arXiv’s 3-year strategic plan (picture below). This plan is broken down into three distinct user categories (readers, authors, moderators) and discusses how each of these users can benefit in three different areas (control, impact, and collaboration). In order to successfully execute this plan, however, arXiv requires our help and wants to hear from scientific communities like the AAS, in order to learn what researchers believe are the highest impact deliverables. 

There are also some specific tasks that the arXiv team is focusing on over the next 18 months. These include distributing some of their classification data to Kaggle, allowing users to contribute to classification algorithms. Additionally, arXiv will be rolling out an update to TeXLive2020 and is actively working on improving their user disambiguation techniques.

Focusing arXiv’s resources to decide which of these goals is completed first is no simple task. Presani highlighted how challenging it is to balance all of the lofty goals of arXiv with their limited resources and discussed how no changes should be rolled out until they are up to arXiv’s high standards, noting that “arXiv was launched in 1991, and when it launched, it was an extremely cutting-edge product and it stayed the same for 30 years. It’s important to find the right balance between being quick and keeping the high quality of the work.”

Interested in helping arXiv execute their vision? There are a variety of ways to contribute. Start by joining arXiv’s user testing or read their blog and news/announcements. They are also looking for volunteers to help with developing a better moderator workflow, and they are soliciting applications for volunteers (if interested, you can send your CV and a motivation letter to [email protected]). Best of all, continue to use the arXiv and engage in discussion with the administrators about what your perfect arXiv would look like in the future.

Laboratory Astrophysics Division (LAD) Plenary Lecture: The Crucial Interplay of Laboratory Experiments, Observations and Theory to Unveil our Astrochemical Origins (by Abby Waggoner)

Our first plenary talk of the day was given by Paola Caselli from the Max-Planck-Institute for Extraterrestrial Physics. Dr. Caselli discussed how laboratory experiments, observations, and theory can be used to better understand the origins of biologically related molecules in space. Life as we know it is made up of amino acids, so many astrochemists seek to understand the origin of amino acids in astronomical environments. Currently, over 200 amino acids have been detected in meteorites, and amino acid precursors have been detected in molecular clouds beyond our solar system. 

To truly begin understanding our astrochemical origins, we begin in a pre-stellar core. Pre-stellar cores lead to the formation of a star and protoplanetary disk. These cores can reach temperatures as low as 6 K, which enables molecules to stick to grains and form an icy coat. 6 K is very cold, so we would expect all of the water in a prestellar core to be frozen out — but water vapor has been detected in these cold regions. These observations led to the question, how is water getting into the gas phase? 

The answer was found using theory. High energy particles (typically protons) accelerated by supernovae and jets from stars, called cosmic rays, can penetrate the ice layers on dust grains. Cosmics rays excite atoms and molecules in the ice, resulting in the production of electrons that can essentially knock the ice into the gas phase and cause chemical reactions to occur. Theory has even shown that the presence of cosmic rays enables the production of complex organic molecules (COMs), such as methanol and other molecules that may eventually play a part in the formation of life. 

Interstellar ices also tell us a bit about the timeline on which molecules froze and were created. Typically, a hydrogen atom (H)  is a single proton and electron, but a fraction of all hydrogen is made up of a proton and neutron, which we call deuterium (D). Deuterium fractionation, or the ratio of H to D, tells us the origins of molecules. For example, the Earth’s oceans have an H/D ratio ten times higher than the Sun’s, suggesting that water on Earth is older than the Sun and comes from meteorites or comets. 

Deuterium fractionation and the formation of COMs in prestellar cores tell us that our chemical origins trace all the way back to molecular clouds. Dr. Cadelli’s talk emphasized that we must use laboratory experiments, theory, and observations in order to understand the chemical inheritance of our solar system. Molecules are everywhere, and we need to work together to understand them.

Press Conference: Galactic Center To & Fro (by Susanna Kohler)

This morning’s press conference explored the center of our galaxy, the Milky Way, “in every which way”, according to conference host and AAS Media Fellow Tarini Konchady.

Christopher Russell (Pontificia Universidad Católica de Chile) opened the session by introducing a new virtual reality app that allows the public to personally experience flying through the galactic center — both through frozen scenes and through 500 years of cosmic evolution, all built from a combination of observations and simulations. Already got a virtual reality setup? The new app, Galactic Center VR, is free through both Steam and Viveport. Have a gaming computer but no VR headset? Typical cost for a headset is a few hundred dollars — which means you can travel to the center of our galaxy for the same price as a plane ticket to travel across the country! Check out a video clip of the VR experience below. Press release

We live in a galaxy where gravity determines how most things move. But could there be regions where the dynamics are instead governed by something else — like magnetic fields? Joan Schmelz (Universities Space Research Association) presents new observations from our favorite flying infrared telescope, the Stratospheric Observatory for Infrared Astronomy (SOFIA), which allow us to map out the streamlines of plasma moving in the central ~15 light-years of our galaxy. These observations show that, despite the strength of the supermassive black hole’s gravity, the plasma motion in the region around Sgr A* is governed primarily by magnetic fields. Results like this one from SOFIA continue to help us reshape our understanding of processes in our galaxy. Press release

A look at our galaxy’s center in radio wavelengths reveals some curious features: long, thin filaments that span distances of up to hundreds of light-years, but are only a fraction of a light-year in width. What are these odd structures, and why do we see them? Shuo Zhang (Bard College) presents X-ray observations of several newly detected filaments that help us to answer this latter question. The new detections lead Zhang and collaborators to hypothesize that the filaments are lighting up in radio and X-rays as they’re bombarded by energetic particles accelerated in the galaxy’s core — possibly by the black hole Sgr A* itself. Press release

galactic center radio

The galactic center contains mysterious filaments seen at radio and X-ray wavelengths. [Slide from Zhang; Image from MeerKAT/SARAO]

Closing out the session, Andrew Fox (Space Telescope Science Institute) presents an exciting possibility: though Sgr A* is quiet now, our supermassive black hole may not always have been so peaceful. Fox proposes that, just 1 to 4 million years ago, the galaxy’s center produced an enormous flash known as a Seyfert flare. This flash of light would have made the night sky look dramatically different for our ancestors millions of years ago! Fox shows that this theory is supported not only by the creation timeline for the Fermi Bubbles (a topic we’ll be touching on in greater detail in tomorrow morning’s press briefing), but also by evidence of photoionization in the matter that makes up the Magellanic Stream, a stream of gas that trails the Large Magellanic Cloud and may have been in the line of fire when cones of ionizing ultraviolet radiation erupted from the galactic center during the flash. Press release

seyfert flash

An intense flash from the galactic center a 1–4 million years ago may have provided our ancestors with a very different night sky. [Gerald Cecil (UNC)]

Plenary Lecture: Satellite Mega-Constellations and the Night Sky: OIR Visibility, Impacts, and Policy; and An Introduction to the RF Spectrum Regulations (by Luna Zagorac)

The first half of this midday plenary was given by Dr. Sandra Cruz-Pol, a Program Leader at the National Science Foundation. Dr. Cruz-Pol underscored the importance of radio frequency (RF) signal management by explaining that if our eyes were able to see all the radio signals that surround us, we couldn’t see farther than a few meters. Furthermore, without regulation of RF channels, all of our communication devices would be rendered unusable due to interference — including cell phones, satellite TV, GPS, hurricane tracking, and more! After all, the RF spectrum is a limited resource, and radio regulations are constantly changing to keep up with new technologies. 

Radio regulations exist at both the international and national levels. Since satellites regularly cross borders, their feeds need to be regulated internationally through the International Telecommunication Union, a UN agency. The ITU splits the world into three regions (with the Americas constituting Region 2), and holds the World Radiocommunications Conference (WRC) every 3–4 years in Geneva. The conference lasts for 4 weeks, and produces both radio regulations via international treaty, which all signatories must abide by, and recommendations, which are typically not mandatory. Nationally, federal assignments are handled by the National Telecommunications Information Administration (NTIA), and non-federal cases are handled by the Federal Communications Commission (FCC). In order for the FCC to adopt a proposal to change RF spectrum regulations in the US, a three-step process is necessary.  

The NTIA also publishes the Frequency Allocation Table (FAT), which shows the signals at each frequency band, including primary allocations in capital letters and secondary allocations in lowercase. Primary allocations grant specific services priority in using the allocated frequency band; if there is more than one, they have equal rights, and have a right to be protected. Secondary allocations involve services that are allocated the same band as primary allocations, but must act to protect and accept interference from primary allocations.

In order to keep up with federal and international regulations, many organizations have Spectrum Managers — including Boeing, Nokia, Google, NASA, NOAA, the Navy, and more. NSF has two Spectrum Managers, who can be contacted for assistance with frequency assignments or questions at [email protected]. Spectrum Managers also have to keep up with the many acronyms of various RF services — such as RAS (radio-astronomy service), SRS (space research satellite service, including near-Earth), ISS (inter-satellite service), and more. 

Dr. Cruz-Pol closed by noting that RF allocation is a complicated topic on which she teaches an entire course, and so many details were left out of her presentations. She also provided listeners with an overview of free resources available online for those interested: 

After that, Mary Elizabeth Moses Professor of Astronomy James Lowenthal of Smith College began his address with solidarity with those suffering from distress over recent events, especially the death of George Floyd and the longstanding harm of institutional racism and police brutality in the US. He then proceeded to show an image of a trail of StarLink satellites, stating: “My life as an astronomer changed early last year when I saw this for the first time.” The launch of StarLink satellites began in 2019, and a total of approximately 1,600 StarLink satellites are scheduled to be in the sky by the end of 2020. The satellites are launched into Low-Earth Orbit (LEO), starting at about 300 km and reaching their final altitude of about 550 km. They are relatively big satellites, about 3.5 by 8 meters long, and they are meant to provide fast broadband low-latency internet coverage worldwide. 

The total number of objects in LEO is close to 20,000, consisting mostly of fragmentation debris, which is generated when larger objects collide and fragment into small pieces — intentionally or otherwise. However, most of these objects are not visible to telescopes and are far from visible to the naked eye. This is not true of StarLink satellites, which have elements that reflect sunlight to Earth and have a brightness magnitude less than 5, most noticeably around morning and evening twilight. The satellites have three phases of life — launch and orbit raise (1–6 weeks), operation (5–25 years), and de-orbit — all of which can impact observations, and different satellites might be in different phases concurrently. Modelling from the Vera Rubin Observatory (formerly LSST) showed that on the night of the summer solstice in Chile, 1–9 StarLink satellites would be visible to the observatory at twilight if orbiting at ~500 km. If the satellites were raised to 1,150 km altitude (still technically LEO), 10–25 satellites would be visible all night long. 

The brightness of the satellites can completely saturate the CCDs of the VRO, leading to tracks of corrupted data. Furthermore, if they are bright enough, they can produce “ghost trails” that are impossible to correct for in the data, rendering more of the image unusable. With the current number of StarLink satellites, VRO can dodge some of these trails in its field of view, but as the numbers rise this will become impossible. Furthermore, some telescopes with wider fields of view are already unable to do this. 

This is a major collision of technologies: the new advanced land-based telescopes and satellite mega-constellations. Dr. Lowenthal notes that, as described by Dr. Cruz-Pol, the protection of the radio sky has been a fortunate fact for decades; however there is no such protection for the optical/infrared sky. While the launch of a satellite requires permissions from many agencies, including the FCC, FAA, and ITU, it decidedly does not require permission from the AAS, the International Astronomical Union, or the International Dark-Sky Association. To suss out the impact of these mega-constellations, the AAS sent out a survey in December 2019 and got answers from all seven continents, including astronomers at observatories like VRO, Gemini, VLT, ZTF, APO, ATLAS, Las Campanas, and more. The answers for current impacts reported a wide range of 0–100% of science lost, with the majority expressing significant concerns, and in some cases significant costs. In the projection of 20,000 more bright satellites (compared to 1,584), 17/23 respondents noted that virtually all their science would be impacted, with 12/23 projecting critical failure of the facility. 

The AAS has been in conversation with satellite operators (primarily SpaceX), and CEO Elon Musk has committed to reducing StarLink’s impact on science to zero. There have been several attempts to minimize brightness, including painting the satellites black (DarkSat), equipping them with visors to shield from sunlight (VisorSat), and re-orienting them so that the sunlight falls on the knife-edge of the satellite, minimizing reflection. However, other operators are planning to launch LEO satellites in the near future, prompted by a $20 billion subsidy from the FCC for such activities, and there is no guarantee that they will be as collaborative as SpaceX. 

Finally, Dr. Lowenthall voiced his opinion, which is that astronomy is facing its most serious threat ever in LEO satellite mega-constellations. He further reflected on the impact of the sky to the human experience, including what the stars and the sky are worth; whose sky is it and who decides; what the value of exploring the cosmos is; and if there are viable alternatives to LEO satellite mega-constellations. Last, he emphasized that the impact of these constellations on the ecosystem is not known, but should be explored — for example, with respect to migratory birds using the stars to navigate. He encouraged astronomers to promote and lead such discussions internationally and with multiple stakeholders, and he then finished with a time-lapse from his own backyard in Massachusetts, asking attendees to spot the StarLink trails.  

National Science Foundation (NSF) Town Hall (by Tarini Konchady)

The National Science Foundation (NSF) town hall featured Ralph Gaume, Director of the Division of Astronomical Sciences (AST); Jim Neff, AST Deputy Division Director; and B. Ashley Zauderer, an AST Program Director whose programs include the Arecibo Observatory and Electromagnetic Spectrum Management.

Gaume’s presentation focused primarily on the impact of COVID-19 on AST and the NSF. A number of NSF-managed observatories have been operating through the pandemic, specifically the National Radio Astronomy Observatory facilities, Green Bank Observatory, Arecibo Observatory, the Global Oscillation Network Group, and Gemini North. The facilities currently idle are Gemini South, the Cerro Tololo Inter-American Observatory (CTIO), ALMA, and the Kitt Peak National Observatory (KPNO). Construction on the Vera Rubin Observatory (VRO) and the Daniel K. Inouye Solar Telescope (DKIST) has also paused. Many of the stalled facilities will require significant work to bring back online, with ALMA in particular posing an enormous challenge. The roadmaps for the next few years regarding VRO and DKIST will also have to be reworked.

The results of the Decadal Survey will also be presented later than anticipated, but the NSF transitioned very smoothly into teleworking right from March. Gaume also mentioned personnel changes in AST and the NSF as a whole. Most notable is the end of France Córdova’s term as NSF Director on March 31 this year. Her likely successor is Sethuram Panchanathan, who was nominated by the President in January. While Panchanathan’s nomination makes its way through Congress, Kelvin Droegemeier (who will be at an AAS 236 town hall tomorrow) has been serving as Acting NSF Director. Droegemeier is also Director of the Office of Science and Technology Policy, which advises the White House.

Gaume wrapped up by highlighting science from the NSF’s facilities, including the new NSF’s National Optical-Infrared Astronomy Research Laboratory — NOIRLab for short. NOIRLab was founded on October 1 last year and consists of all the NSF’s nighttime ground-based observatories in addition to the Community Science and Data Center. The rest of the science highlights can be found in the Twitter thread linked below:

On the budget side, AST and the NSF are doing reasonably well. As usual, the President’s Budget Request for the fiscal year 2021 decreased NSF funding, but also as usual, Congress appropriated funds for the NSF at a level higher than the Request level. Legislature to watch includes the Securing American Leadership in Science and Technology Act, introduced by Republicans on the House Committee of Space, Science, and Technology, and the Endless Frontier Act, spearheaded by Senate Minority Leader Chuck Schumer. The latter would significantly change the operations of the NSF and other federal organizations.

Gaume then handed things off to Neff, who focused on the status of various AST grants. Neff emphasized that the grants and programs under AST were heavily informed by community input. The pandemic has caused disruptions to several grant programs, but AST is working to remedy this. Astronomy and Astrophysics Research Grants are currently being awarded with a success rate of roughly 1 in 5, which is standard. Neff reminded attendees of the deadlines for different AST grants as well as grants in other divisions that astronomers could be eligible for. These grants include opportunities in data science and computer engineering. Neff wrapped up by introducing the new guide to NSF proposals and as a resource.

Zauderer wrapped up the town hall by discussing the NSF’s efforts on protecting spectrum use for astronomy. She referred attendees to the plenary by Sandra Cruz-Pol and James Lowenthal earlier today for a deep dive into the issue. The NSF would like to expand its efforts in radio spectrum management and extend these efforts to optical wavelengths. Zauderer mentioned that private companies like SpaceX have been amenable to mitigating harm to astronomy. To that end, she highlighted the Satellite Constellations 1 Workshop, a joint effort between the AAS and NOIRLab that will bring together “astronomers, satellite operators, dark-sky advocates, policy-makers,” and others to discuss the impact of satellite constellations. She also highlighted the NSF’s Spectrum Innovation Initiative, which would offer funding to parties interested in this issue.

Space Telescope Science Institute (STScI) Town Hall (by Amber Hornsby)

Opening the Space Telescope Institute (STScI) town hall today was the director of STScI, Dr. Kenneth Sembach, who started with a general update of operations. The key take-away message from the director is, “we are here to support and help you advance scientific discovery.” Naturally some activities have been impacted by COVID-19, but things are slowly starting up again with seminars, proposal evaluations, and more being re-imagined for online platforms. 

Next on the agenda for Sembach was discussion of a very exciting project — the Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES). With a grand total of 1,000 orbits, this is the largest single Hubble Space Telescope (HST) program ever executed, and it has two primary objectives: (i) 500 orbits to extend the spectroscopic library of O and B stars of low metallicity and (ii) 500 orbits to create a spectroscopic library and time monitoring of T-Tauri stars (younger than 10 Myrs). The first data release of the Small and Large Magellanic Clouds will be in September 2020. 


Illustration of NASA’s WFIRST telescope, now the Nancy Grace Roman Space Telescope. [NASA]

The final, and possibly most exciting, part of Sembach’s talk was presenting the Wide Field Infrared Survey Telescope (WFIRST) as the Nancy Grace Roman Space Telescope. “NASA could not have chosen a better person,” said Sembach, because “she loved the universe.” This is where the STScI and NASA asks for help from the community. “We want and need to know how you will use the Nancy Grace Roman Space Telescope.” Please participate in an open community survey by June 15. 

Moving on to a big problem in modern astronomy — Dr. Joshua Peek discussed large data sets and improving their accessibility. As new instruments come online and take an unprecedented amount of data, it becomes more and more challenging to ensure everyone can access the archived data and that they can do exciting science with it. STScI has already started tackling this problem with a NASA-funded project, the Milkulski Archive for Space Telescopes (MAST), which collates data from the HST, the Transiting Exoplanet Survey Satellite (TESS), and Kepler

So far, astronomers are already making great use of MAST to write an impressive number of papers, which has highlighted another trend in astronomy: the number of institutions represented on a paper. The median number of institutions for every paper published using MAST data is now 5. This represents another problem facing many groups: the problem of each member being able to access data sets and work on them simultaneously. Here, Peek introduces the Time series Integrated Knowledge Engine, otherwise known as T.I.K.E.

T.I.K.E is a public, cloud-based Jupyter lab environment which contains pre-installed software for interpreting time series data, the kind associated with the study of exoplanets. Not only are your usual python packages like Numpy and Scipy built in alongside key packages for astronomy, like Astropy, but T.I.K.E also includes specialised packages created to work with time series data such as Exoplanet. All of this is useful, but what makes T.I.K.E next-level is access to TESS and Kepler data through the platform, the built-in notebooks and shared repositories for collaborations. Through T.I.K.E, the learning curve to participate in astronomy will be reduced, which will “accelerate science” and enable scientists to “find more stuff”, more quickly. T.I.K.E will be available sometime this summer. 

Next up, Dr. Karoline Gilbert presents ‘Hundreds of Hubbles in the 2020s: realising the scientific potential of the Roman Space Telescope Archive’. Having recently passed the “formulation” phase of the mission, we’re now moving towards “implementation,” meaning the design has been finalised, thus hardware is now in development, and flight detectors are being built and delivered. 

With a Hubble-sized primary mirror of 2.4 meters, we can already anticipate beautiful Hubble-quality images from the Roman Space Telescope when it is launched within the decade, but what is particularly revolutionary is its field of view. Having a larger telescopic view allows large areas of sky to be mapped faster. For example, the Roman telescope can measure the complete satellite and cluster populations of a galaxy, capturing the extent of the dark matter halo, with Hubble-like sensitivity and resolution in one pointing. For nearby galaxy surveys, like the Panchromatic Hubble Andromeda Treasury (PHAT), the Roman Telescope can map the same region almost 1,500 times faster. 

Furthermore, data from the Roman Space Telescope will be publicly available with no proprietary period, via a T.I.K.E-like environment. This is an exciting step forward towards a more open and accessible field of astronomy, which will enable an impressive amount of science to be done by astronomers all over the globe. Currently, the team predicts proposal opportunities will be available at the beginning of 2021 and invites astronomers to participate in a virtual conference focused on the future of galaxy formation and evolution studies in October. 

To close out the town hall, Dr. Louis Strolger reports on the recent HST proposal cycle 28 and the changes implemented in the review process. To address the COVID-19 impact, the proposal deadline was extended and the review was completed entirely via virtual platforms. Another recent change that also occurred for the last two cycles was a dual-anonymous review hiding the identities of proposers throughout the scientific ranking phase. This process is having an important impact on the gender diversity of proposers.

Over the last three cycles, the gap in proposal acceptance rate between male and female PIs has decreased from an average of 5% to 1%, with a predicted increase of female-led proposals of 0.5% per year. Furthermore, the number of PIs being awarded programs for the first time is also on the up, suggesting the dual-anonymous process is allowing the next-generation of scientists to get telescope time. Due to its success, the dual-anonymous review process will continue to be implemented and will also be used for James Webb Space Telescope (JWST) proposals, which are expected to be due in late fall. 

Press Conference: Planets, Exoplanets & Brown Dwarfs (by Haley Wahl)

The second press conference of the day focused on planet-like objects! 


Phobos as seen by Mars Express. [G. Neukum (FU Berlin) et al., Mars Express, DLR, ESA; Peter Masek]

First up was Matija Cuk from the SETI Institute speaking about Mars’s moons. The planet Mars has two moons: Phobos and Deimos, both of which were previously thought to be captured asteroids. However, by looking at the orbital inclination of Deimos, this team found evidence of a past Martian ring that created what is now Phobos — and that ring was formed from a “proto-Phobos” which was 20x the current mass of Phobos. This, his team believes, is only the latest case in a cycle of a moon becoming a ring and then the ring becoming a smaller moon. Press release

Next up was Fritz Benedict from the University of Texas, Austin to talk about calculating the mass of the recently identified, nearby planet Proxima Centauri c. By revisiting 25-year-old Hubble data, combined with some newer results from 2020, his team finds that the mass of Proxima Centauri c is either that of 18 Earths or 7 Earths, depending on which measurements are included in the calculations. Though there is still work to do, this finding shows that you can indeed find new results from old data. Press release

brown dwarf disk

Illustration of a brown dwarf surrounded by a disk. [NASA/William Pendrill]

The third speaker was amateur astronomer Paul Benni from the Acton Sky Portal. He discussed the first discoveries of the Galactic Plane Exoplanet Survey (GPX). The first of these new discoveries is KPS-1b: the first transiting exoplanet (a hot Jupiter) discovered using an amateur astronomer’s wide-field CCD data. Another major discovery was GPX-1b, a transiting brown dwarf orbiting an F star. This was not detected by TESS algorithms because the host star was <1 arcmin away from a really bright star, so it diluted away the transit signal. The final discovery: a pre-cataclysmic binary with unusual chromaticity of the eclipsed white dwarf! Read more about Paul’s work in his paper.

The final speaker of the press conference was Maria Schutte (@maria_schutte), a PhD student at the University of Oklahoma. She discussed the citizen science project Disk Detective, which allows people at home to find new planet-like systems. This project led to the discovery of W1200-7845, an especially young (~3.7 Myr), nearby (332 light-years) brown dwarf disk! W1200-7845 provides us with a unique opportunity to study a potentially planet-forming disk around a nearby brown dwarf. To learn more, follow @diskdetective on Twitter. Press release

Plenary Lecture: The Atacama Cosmology Telescope and the Simons Observatory: The Millimeter-Wave Sky from Chile (by Amber Hornsby)

For the final plenary of day 2 at AAS 236, Prof. Jo Dunkley (Princeton University) presents the millimeter sky as viewed by the Atacama Cosmology Telescope (ACT) in Chile, and plans for a next-generation cosmology telescope, the Simons Observatory (SO). Throughout the plenary, there is a focus on the cosmic microwave background (CMB) and what it tells us about the universe; however, we also learn about bonus discoveries that can be made with detailed surveys of the millimeter sky. 

The CMB is often referred to as the “afterglow of creation” because we’re looking at the oldest photons in the universe. Initially, the universe was a hot, opaque soup of interacting photons and baryons. After 380,000 years, the universe had expanded and cooled enough for photons to escape, and this is the remnant light we can observe today. When observed for the first time in 1964, it appeared to act like a perfect, uniform blackbody with a peak temperature of 2.74 K and peak wavelength of around 2 mm. But, thanks to improved measurements, we now know there are actually tiny temperature fluctuations in the CMB. 

The temperature map, created using data from the Planck space telescope, is a nice snapshot of the physics of the universe at a redshift of z = 1,100. The intensity of the CMB mainly tells us about the density of the photon-baryon plasma, where hot spots (shown in red) represent denser regions. Dunkley explains how, if the map is decomposed in terms of angular scale, we can plot the amount of “bumpiness”, the so-called power spectrum of the sky. Given this, we can theoretically predict different model universes, containing different initial ingredients and conditions until our predictions fit the observed data. The best-fit model to Planck data is given by a Lambda-Cold-Dark-Matter (LCDM) cosmological model requiring three ingredients and two initial conditions. 

As CMB photons travel through the universe, they encounter galaxies, hot electrons and more, which alter the photons in some way. For example, CMB photons are very sensitive to massive objects, which results in the lensing of the CMB. It is further distorted by the thermal and kinetic Sunyaev-Zel’dovich (SZ) effect. The thermal SZ effect is where hot electrons scatter the CMB, causing a shift in its observed spectrum, whilst the impact caused by the momentum of high-energy electrons is characterised by the kinetic SZ effect. It is important to characterise these effects to get an accurate picture of the CMB.

However, something that CMB enthusiasts can forget is the “wealth of information” contained within surveys of the millimeter sky beyond the CMB. Dunkley points to observations of polarised dust taken by Planck. Although dust contaminates our CMB signal, we can infer the orientation of the magnetic fields in our galaxy through the alignment of dust grains by simply rotating the polarisation signal by 90 degrees. This is because dust grains align themselves perpendicular to the magnetic field. But this is only the start. Surveying the millimeter sky addresses other key astrophysics questions, such as (i) how long did reionization take? (ii) where is Planet 9? (iii) is the accelerated expansion of the universe just Lambda? 

Dunkley now introduces ACT, and how it builds on Planck’s legacy. ACT has been operating since 2007 and its third-generation instrument has around 5,000 detectors. There are a few differences between ACT and Planck, such as ACT only mapping 40% of the sky and being ground-based. However, ACT data have 3 times less noise than Planck data and are much better resolved. In recent ACT maps, this has uncovered radio galaxies (blazars) and galaxy clusters through the SZ effect. Moreover, ACT has observed the largest-ever SZ galaxy cluster sample containing over 4,000 clusters!

Additionally, ACT has captured unprecedented views of the polarised sky at 2 mm, the signal size of which is known as the E-mode component of polarisation. Here, white represents higher polarisation on the grey-scale image. We can also create a power spectrum based on ACT data which, combined with data from the ground-based telescopes POLARBEAR and the South Pole Telescope (SPT), can provide an independent calculation of the contentious Hubble constant. A paper on this new result is currently in preparation. 

Sadly, Dunkley reveals, we have hit an upper limit on the number of detectors we can fit in the telescope. This is important because without more detectors, we cannot make further reductions in the noise in our observations. We thus need to consider a new telescope — Simons Observatory. Already under construction, the 6-meter-primary telescope will live alongside ACT in Chile and will house over 30,000 transition-edge sensor detectors. 

This impressive telescope will have a huge impact on the millimeter community, providing new opportunities to participate in transient science through synergy with multiple surveys. SO plans to track thousands of variable active galactic nuclei on a daily/weekly/monthly basis at 1–10 mm wavelengths. With an observing timeline of 2023–28, SO will overlap with the Vera Rubin Observatory, the Dark Energy Spectroscopic Instrument (DESI), and Euclid, enabling observations to be completed simultaneously at different wavelengths. In addition to the substantial improvements in CMB observations, including the potential for a glimpse of the elusive B-mode component of the polarised CMB, SO will also observe 30,000 high-redshift, dusty galaxies and 20,000 clusters.

In her closing remarks, Dunkley reminds us that there is “so much to learn from wide-field surveys of the millimeter sky.” We can learn about our galaxy, transient sources, AGNs, and my favourite, the CMB, which gives us a “unique view of the early universe.” ACT scientists are looking forward to sharing new data and software with the astronomical community — so keep an eye out for upcoming press releases.

About Astrobites

This post was written collectively by multiple members of the Astrobites team. Meet the authors of Astrobites.

Discover more from astrobites

Subscribe to get the latest posts to your email.

Leave a Reply