Editor’s Note: This week we’re at the 234th AAS Meeting in St. Louis, MO. Astrobites and AAS Nova will be working together to publish updates on selected events at the meeting this week; the usual posting schedule for AAS Nova will resume next week.

Plenary Lecture: Transiting Exoplanets: Past, Present, & Future (by Susanna Kohler)

The remarkable thing about planet transits, says Joshua Winn (Princeton University), is the incredible wealth of information we can obtain from simple blips of light. “Transits are by far our richest source of information about planets,” he pointed out in the opening of his plenary — transits can reveal not just properties like masses or periods of planets, but also surprising details like the composition of planet atmospheres or the obliquity of the host star.

Transit data from Kepler (bottom) compared to data from a ground-based telescope of comparable size (top).

The field of transit study has a long history, but it exploded in 2009 with the launch of the Kepler mission. Kepler studied a small patch of sky just above the galactic plane for roughly four years, building up a large sample of planet candidates that could be used to statistically explore the population of exoplanets in our galaxy for the first time. The data quality possible with Kepler was a huge step up from the observations we’d gathered from ground-based telescopes — which allowed for the detection of additional features in transit light curves that could tell us more about unusual systems.

Winn shared with us a few of his favorite weird Kepler systems, which include:

• Kepler-89, in which we observe a planet being eclipsed by another planet as the two bodies transit their host star
• Kepler-36, a system challenging our understanding of planet formation, since it contains two planets that lie at very nearly the same orbital radius but are vastly different in nature: one is a dense, rocky super-Earth, whereas the other is a fluffy, gaseous mini-Neptune
• Kepler-16, a star with a bizarre light curve that turns out to be perfectly explained by a circumbinary planet transiting across the faces of both of its hosts

Comparison of TESS’s planned coverage of the sky (blue) compared to Kepler’s coverage (yellow).

“As much as we love the Kepler mission, it did have one tragic flaw,” Winn lamented. “It didn’t cover the whole sky.” Even with Kepler’s extended K2 mission, it only accessed about 5% of the sky. This brings us to the current leader in exoplanet transit detections: the Transiting Exoplanet Survey Satellite (TESS).

TESS, launched 14 months ago, is designed to tile almost the entire sky during its 2-year primary mission; at this point, it’s already mostly through observing the southern hemisphere. TESS’s data — which is all made public immediately — includes two types: 30-minute full-frame images, and 2-minute subimages tracking 100,000 selected stars. Though TESS spends less time looking at each individual patch of sky, it will discover short-period transiting planets around a huge variety of stars throughout the galaxy. As of this morning, Winn reported, the number of TESS planet candidates stood at ~700 — and we can expect many more to come!

Past, current, and upcoming missions contributing to exoplanet exploration.

What’s the future of exoplanet study look like? TESS will serve as a bridge between Kepler and a number of upcoming missions. Targets selected by TESS can be followed up for atmospheric studies with the James Webb Space Telescope (JWST) and radius measurements with the CHaracterising ExOPlanets Satellite (CHEOPS). And the Wide Field Infrared Survey Telescope (WFIRST) stands to revolutionize exoplanet exploration for microlensing in the same way that Kepler revolutionized the field for transits.

Winn concluded with a message for any students in the audience deciding on a field of study: with transiting exoplanets, you have a rare opportunity to join an exciting field with few barriers to entry, massive amounts of data, and a very clear agenda for the next decade. It’s definitely an option worth considering!

Don’t forget that you can learn more about Winn and his work by checking out the interview conducted by Mike Foley here.

Press Conference: Even More Sun & More Milky Way (by Susanna Kohler)

This morning’s conference is following a familiar theme: even more studies about the Sun and the Milky Way! The first two presentations of the day focused on a favorite solar topic: predictions about the solar cycle and its impacts on Earth.

When data is scaled and stacked by terminator-to-terminator solar-cycle length, patterns become evident in factors like El-Niño behavior (ENSO), galactic cosmic-ray measurements (GCR), and sunspot number (hSSN).

Is there a relation between the solar cycle and large-scale weather patterns on Earth, like El Niño? Robert Leamon (University of Maryland & NASA Goddard SFC) argues yes — but it’s not tied to local solar-activity minima or maxima. Instead, he suggests that it’s the termination of each solar cycle — which occurs every ~11 years on average, but varies in exact timing — and the corresponding decrease in cosmic-ray flux that drives the swing on Earth from El Niño to La Niña. Leamon and collaborators use a signal processing method to analyze past data and project when the current cycle, Cycle 24, will terminate, finding that the termination will occur in April 2020 and drive the El-Niño-to-La-Niña transition shortly thereafter. Leamon concluded by emphasizing that this connection does not mean that the Sun is the cause of global warming; indeed, this coupling between the Sun’s activity and Earth’s atmosphere is only possible because climate change has already occurred.

Kitiashvili and collaborators predict that the next solar cycle will be significantly weaker than previous ones.

Next up, Irina Kitiashvili (NASA Ames Research Center) introduces some predictions for long-term solar activity. By using a new technique that relates observations of the magnetic fields on the Sun’s surface to the state of the solar dynamo deep in the Sun’s interior, and by taking into account uncertainties in the data and the dynamo model, Kitiashvili and collaborators generate predictions of the future state of the Sun. They, too, estimate that the next solar cycle will begin in 2020, and they predict that the next solar maximum will be 30–50% lower than the most recent one — making it the weakest cycle of the last 200 years. Press release

Green circles mark citizen-scientist-identified “yellowballs”, intriguing young star-forming regions. [Milky Way Project]

It’s not often that you get confirmation of a prediction you made a decade ago; Sukanya Chakrabarti (Rochester Institute of Technology), however, is having that experience now. Ten years ago, she and collaborators used dynamical analysis to predict the presence of a large, dark-matter dominated dwarf galaxy that crashed into the Milky Way and produced large ripples seen in the gas of our outer galaxy. The problem? They couldn’t find a dwarf galaxy that matched their predictions. Now, a decade later, Chakrabarti may have found the culprit at last.

Gaia data recently revealed a new dwarf galaxy, Antlia 2, that has very few stars but a large amount of dark matter. Though similar in extent to the Large Magellanic Cloud, Antlia 2 is two orders of magnitude fainter! Chakrabarti and collaborators have shown that the properties and position of this galaxy beautifully match the predictions for the perturber they think smashed into the Milky Way long ago (see the gif below for the simulation of this interaction; gas is shown on the left, stars on the right). As an added test, they predict precisely where Antlia 2’s stars should be located in the future if this is, indeed, their missing galaxy. We can check whether they’re right in a year or two with the next Gaia data release! Press release

Plenary Lecture: Cosmological Inference from Large Galaxy Surveys (by Susanna Kohler)

The most surprising cosmological discovery of recent decades is the accelerating expansion of the universe — an unexpected outcome that has simultaneously driven theorists to develop new models and inspired a new generation of large cosmological surveys. These surveys will each gather a wealth of data — perhaps higher-precision measurements of the cosmic microwave background radiation, or better spectroscopic and photometric galaxy statistics — that can be individually used to provide constraints on the universe’s composition and evolution. But Elisabeth Krause (University of Arizona) asserts that the most stringent cosmological constraints will be obtained when we analyze these data with a careful eye for systematics, and when we combine the information from these different probes.

Current and upcoming photometric cosmology surveys. Can we combine information from these different probes to obtain tighter constraints?

How do we do this? First, it’s important to note that this upcoming decade of large surveys marks a new era. Gone are the days in which observations were easily analyzed, maps and catalogs easily produced, and lone geniuses were easily able to develop cosmological models from those products. In the current era of large-scale projects, Krause says, this model is no longer possible; now entire teams of people are needed to process the enormous volumes of data and jointly draw useful conclusions from them.

This new collaborative model is certainly evident in the Dark Energy Survey (DES) project, a visible and near-infrared wide-field survey that imaged millions of galaxies to produce a dataset that astronomers can use to learn about the growth of large-scale structure in the universe. But the key to good analysis is to properly account for systematics — which can include things like experimenter bias. In a collaboration of several hundred people, how do you make sure that eager scientists hoping for results for conferences, for instance, don’t end up unintentionally biasing the results? DES solved this problem by using complex blinding schemes that prevented the experimenters from seeing the data as they worked. Only once they all signed off on the conclusion of the analysis were they able to “open the box” and see what constraints came out.

The LSST collaboration already consists of more than 600 people.

Strategies like this will be even more important in the future, as we move from datasets containing a few million galaxies to many billions of galaxies once WFIRST, Euclid, and the newly renamed Vera Rubin Survey Telescope (formerly LSST) come online, with correspondingly larger collaborations. But if we analyze these upcoming observations with careful attention to systematics, and if we combine the constraints of these surveys in thoughtful ways, we will soon have a better understanding of the nature of our universe than ever before.

Press Conference: Cold Quasars & Hot Cosmology (by Susanna Kohler)

Artist’s illustration of a bright blue quasar clearing the gas and dust out from around it. [Michelle Vigeant/University of Kansas]

Fun side story: the upcoming merger of the Milky Way and Andromeda will likely proceed in exactly this way. Though both our galaxy’s supermassive black hole and Andromeda’s are quite anemic, the influx of fuel from a merger will cause the resulting, merged black hole to light up as a stunning quasar, dominating the night sky and eventually expelling the gas of the galaxy. No new stars will form after this point, so “this will spell the beginning of the end for life in the Milky Way,” cautions Kirkpatrick. Of course, she continues, this will be in ~3–4 billion years and will be around the time when the Sun evolves into a red giant, so we may have other, more pressing concerns at the time. Press release

The other two presentations of the session both addressed the same problem: the tension between local and global measurements of the Hubble constant (H₀), a value that describes the rate of expansion of the universe. The best way to measure this constant in the local universe is to use the distance ladder to measure the distance to and recession speed of local galaxies. The most recent study using this approach gives a value for the Hubble constant of H₀ = 74.03 ± 1.46 km/s/Mpc. Other experiments — like Planck — have instead measured H₀ on global scales. By determining H₀ in the early universe using observations of the cosmic microwave background (CMB) radiation, we can then evolve this value forward to present-day using ΛCDM cosmology, our best-guess model describing our universe’s evolution. This technique produces a value for the Hubble constant of H₀ = 67.4 ± 0.5 km/s/Mpc. The local and global values are therefore in tension: there’s a 9% unexplained difference between the measurements. Is this difference due to systematics? Or is there new physics involved that we haven’t yet considered?

In this computer simulation, we see a region of the universe wherein a low-density “void” (dark blue region at top center) is surrounded by denser structures containing numerous galaxies (orange/white). Could such a void explain inconsistencies in the measured Hubble constant? [TNG collaboration]

So if local voids are out, it would seem that perhaps new physics is, indeed, needed to resolve the problem. Maurice Van Putten (Sejong University) has an idea: what if the fact that the universe is evolving means that ΛCDM cosmology isn’t the best model at all orders? If we take into account deviations from ΛCDM predicted by quantum cosmology, then Van Putten shows that this new model applied to CMB measurements produces a global value for H0 that nicely matches the value found from local measurements. Voila, tension is gone! It seems surprisingly simple (though the math really isn’t!), but comparison to future observations should provide a check of this theory.

Karen Harvey Prize Lecture: Where Do Solar Eruptions Come From? (by Susanna Kohler)

The final plenary of the day was given by Anthony Yeates (Durham University), who is the recipient of this year’s AAS/SPD Karen Harvey Prize, an award that recognizes early-career individuals who have made a significant contribution to the study of the Sun. In Yeates’s case, his contribution is in the form of work advancing our understanding of “how the Sun’s magnetic fields originate, evolve, and govern the dynamics of the solar corona,” and he was ready today to give us his take on where solar eruptions come from.

The dark structures visible against the Sun’s disk are solar filaments.

Yeates argued that the key to understanding solar eruptions is to understand how magnetic helicity is injected into and removed from the Sun’s atmosphere. He opened by showing us images of enormous magnetic filaments — dark, string-like structures visible against the Sun’s disk. These magnetically-confined channels of cool gas are what eventually give rise to eruptions and flares, and the twisted and helical magnetic fields that govern them become evident when you look at them closely. Magnetic helicity is the measure of how tangled, twisted, and linked these fields are.

Over the next half-hour, Yeates built up a compelling picture of how energy is freed from the Sun’s surface and expelled into space in an eruption.

• Step 1: Magnetic helicity is injected into the Sun’s corona by motions on the surface of the Sun. There are multiple components to this: the Sun’s rotation generates helicity, and more is added as the footpoints of magnetic field lines wander via diffusion, tangling the fields.
• Step 2: Once helicity has been added into the atmosphere, it accumulates at polarity inversion lines, locations where the magnetic polarity swaps. This build-up allows field lines to get close together — exactly what’s needed for magnetic reconnection to occur.
• Step 3: Helicity is removed from the atmosphere via coronal mass ejections. Sudden eruptions (likely following reconnection) throw some of this tangled magnetic field out into space, removing it from the Sun’s atmosphere.

Magnetic fields on the Sun are complicated!

Currently, Yeates said, observations and models are in good agreement, leading to general acceptance of this paradigm. But we still have plenty more work to do! The ultimate goal, of course, is to be able to predict when eruptions will occur. We’re certainly not there yet — Yeates earned a laugh when he described the current state as “we can predict them after they happen” — but this understanding of how energy makes its way from the solar surface into eruptions is a huge step in the right direction.

You can read more about Yeates in the interview conducted by astrobiter Mia de los Reyes here.

Editor’s Note: This week we’re at the 234th AAS Meeting in St. Louis, MO. Astrobites and AAS Nova will be working together to publish updates on selected events at the meeting this week; the usual posting schedule for AAS Nova will resume next week.

Laboratory Astrophysics Division (LAD) Plenary Lecture: The Role of Dust in the Molecular Universe (by Kerry Hensley)

Grand Prismatic Spring in Yellowstone National Park. [Clément Bardot]

These discoveries give us a hint — and hope — that life may be widespread in the universe, able to withstand even the harshest environments. Life on Earth is built from organic molecules, which are composed of carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur. How did the organic molecules that life is built from end up on Earth in the first place? They can either exist in the material that the Earth formed from (starting with tiny dust grains in the Sun’s protoplanetary disk) or they can be delivered to the planet later on in the form of asteroids and comets (particularly the ones that were scattered into the inner solar system during the Late Heavy Bombardment).

An example of how the composition of chondrites (stony meteorites) can affect the composition of a planet’s
atmosphere.

The chemical makeup of this material is important because it determines, in part, the composition of Earth’s atmosphere. For example, if most of the material has a “reduced” composition, the atmosphere will tend to be methane-rich. If most of the material has an “oxidized” composition, the atmosphere will tend to be nitrogen-, carbon-dioxide-, or water-vapor-rich, depending on the temperature. It’s really easy to make amino acids (important for life!) in the presence of methane, and really hard to make them without, so the composition of the atmosphere is crucial.

A lot of the exciting chemistry happening in the interstellar medium that has important implications (much later on) for planetary habitability takes place on icy dust grains. Dust grains are important because they provide a surface onto which atoms and molecules can stick, move around, and react to form other compounds. The timescales are a lot longer than in the gas phase, where you basically get a split-second chance at a reaction during a collision. Dust grain-surface chemistry creates a lot of molecules we care about like oxygen, carbon dioxide, and methanol — we likely have dust to thank for life on Earth!

Dr. Tielens closed his talk with an encouragement for laboratory astrophysicists everywhere: everything you can study in the lab will be relevant somewhere in the universe — it’s your job to find out where!

Press Conference: Spiral Galaxies Near and Far (by Susanna Kohler)

Artist’s impression of the Milky Way galaxy. [NASA]

What’s going on at the very heart of our galaxy, in the central ~15 light-years? This region contains a tilted disk of gas and dust rotating counterclockwise around our galaxy’s supermassive black hole, Sgr A*. This ring is best observed at ~50 µm, a wavelength that can only be accessed from high altitudes; luckily, we’ve got SOFIA, our favorite flying observatory, on the job.
SOFIA’s HAWC+ instrument obtained both images and polarimetry — measurements of magnetic fields — of the central ~15 light-years of the galaxy. C. Darren Dowell (Jet Propulsion Laboratory) showed us the results: a spectacular map of the streamlines tracing the magnetic field within the heart of our galaxy (see the cover image at the top of the page). HAWC+’s measurements reveal a beautiful spiral structure to the dust that indicates the magnetic field is strong enough to channel material into orbit around the black hole. This subtle redirection may be enough to explain why our black hole is unusually quiet: magnetic fields might be preventing Sgr A* from getting a proper meal! Press release

Spiral arms will have different apparent angles at different wavelengths as stars propagate away from spiral density waves.

The next two speakers both described tests of the dominant theory for what causes spiral structure in galaxies: density wave theory. According to this model, density waves propagate through the disk of a galaxy. Gas and stars don’t remain stationary relative to these spiral waves, though; instead, their rotation speed is set by their distance from the center of the galaxy, and this speed matches the pattern speed of the density wave only at one location, known as the co-rotation radius. Inside this radius, newly formed stars caused by compression of the gas will disperse ahead of the density wave; outside of the co-rotation radius, they trail behind the wave. According to the density wave theory, the shape of a spiral arm will therefore look different at different wavelengths: bluer wavelengths will trace the younger stars distributed close to the density wave, appearing as a more radial arm, whereas redder wavelengths will trace the older stars that have trailed further ahead of and behind the density wave, appearing as a more angled arm.

To test the picture of density wave theory, a team of scientists looked for these differences in arm shape across different wavelengths for ~30 galaxies. Daniel Kennefick (University of Arkansas) presented the results: the arms were indeed angled differently at different wavelengths, exactly as predicted by density wave theory. Kennefick remains cautious, however: this seems like a triumph for the density wave model, but other research groups have found opposing results. As always, more work remains to be done!

Shameer Abdeen (University of Arkansas) and collaborators took a different approach to test density wave theory: they attempted to measure the co-rotation radius for a sample of ~20 spiral galaxies. They did this by tracing out the galaxy’s spiral arms at different wavelengths, and then identifying the location where these arms crossed over one another. The good agreement of their results with other, independent measures of the co-rotation radius provides additional confirmation that density wave theory is a solid model.

In the Spiral Graph citizen science project, volunteers trace out the spiral arms of galaxies. These tracings are stacked to produce a final map of a galaxy’s arms, which can then be used in the hunt for intermediate-mass black holes.

Abdeen and collaborators were able to trace out the spiral arms of their sample by hand, but what do you do if you have a sample of galaxies larger than ~20? Patrick Treuthardt (North Carolina Museum of Natural Sciences) has the answer: enlist the help of citizen scientists! Since computers have a hard time picking out spiral arms in low-contrast images, Treuthardt and collaborators looked to humans, who are inherently quite good at identifying patterns — even in faint images. To enlist enough humans to trace the spiral arms of a sample of thousands of spiral galaxies, the group set up a citizen science project based on the Zooniverse platform: Spiral Graph. In this project, anyone can go look at images of galaxies and mark where you think their spiral arms lie. Tracings of multiple citizen scientists are then averaged to produce a map of each galaxy’s arms.
Beyond being a fun way to kill time, this exercise has a purpose! Once we’ve mapped the arms of these galaxies, we can easily estimate their pitch angles. Intriguingly, how tightly these arms are wound correlates with the mass of the black hole hosted at the center of the galaxy. By selecting galaxies with very loose spirals, the team hopes to identify those galaxies most likely to host elusive intermediate-mass black holes (IMBHs). Astronomers only know of a dozen or so confirmed IMBH candidates thus far — so go do some spiral tracing and contribute to the discovery of more!

Plenary Lecture: The Tools of Precision Measurements in Exoplanet Discovery and Characterization: Peeking under the Hood of the Instruments (by Kerry Hensley)

Suvrath Mahadevan (Penn State University) gave the audience a peek “under the hood” of the highly precise instruments bringing us exoplanet detections and atmospheric characterizations. Thanks to missions like Kepler and the Transiting Exoplanet Survey Satellite (TESS), we’ve discovered thousands of exoplanets, with many more on the way. As a result, some of our focus has shifted from detection to characterization — we want to know what’s in the atmospheres of these planets and whether they might be habitable or not.

A depiction of what a shift corresponding to a velocity of 10 cm/s looks like on a detector. The silvery dots are individual silicon atoms.

What will it take to detect small, rocky planets and learn about their atmospheres? Really, really, really precise instruments. Currently, we can measure radial velocities of about 1 m/s. This is pretty good, but we’d like to get down to the tens-of-centimeters-per-second or centimeters-per-second level to detect lots of Earth-mass planets around faraway stars. That’s easier said than done, though! A velocity of 10 cm/s corresponds to a shift of just a few lattice-spacings on a detector — that’s 1/6000 of a 10-micron pixel!

What do we need in order to get down to that level of precision? A lot of things need to come together to make it happen: a really good spectrograph, a high-performance detector, a way of calibrating the instrument (e.g. laser combs), precise temperature and/or vacuum control of the environment that the instrument and detector are housed in, and an excellent data reduction pipeline, to name just a few.

Mahadevan highlighted a couple of current instruments: the Habitable Zone Planet Finder (HPF) on the Hobby-Eberly Telescope, and NEID, which will be installed on the WIYN telescope at Kitt Peak. HPF has given us the highest-precision near-infrared radial velocities ever reported. (As an aside, things get really interesting in the infrared: the act of reading out the detector warms it enough that the detector itself becomes a source of noise. There are also crystalline lattice defects that cause shifts in the quantum efficiency of the detector at sub-pixel scales, which can’t be removed through flat-fielding.)

Let’s say we can overcome these issues and build spectrographs and detectors capable of detecting the subtle shift in spectral lines corresponding to velocities of ~10 cm/s. We still have a problem: getting our instruments down to 10 cm/s won’t help us if we can’t disentangle the competing effects of transiting planets and solar activity. So, there’s still plenty of work to be done on the science side as well as the instrumentation side, both of which will help us in our quest to track down Earth-like planets.

Press Conference: More Sun & More Milky Way (by Susanna Kohler)

The afternoon press conference presenters are ready to go under the direction of AAS Media Fellow Kerry Hensley!

This afternoon’s press conference was hosted by AAS Media Fellow and astrobiter Kerry Hensley, and it promised more exciting results from our nearest star and galaxy.

First up, Kevin Reardon (National Solar Observatory) presented observations of the Sun from the millimeter/submillimeter powerhouse ALMA. The wavelengths probed by ALMA’s 64 antennae provide views of different layers of the Sun’s chromosphere, the atmospheric layer sandwiched between its cooler surface (the photosphere) and its hotter outer atmosphere (the corona). As “the gateway to the corona”, the chromosphere may eventually provide us with information about how heat is transferred from deep in the Sun’s interior to its outermost layers — if we can understand observations of it! Reardon and collaborators showed that ALMA’s 3.1-mm images of the Sun showed striking similarities to the more easily obtained optical images made using the Hα emission line (656.3 nm). This discovery will help us to better interpret Hα images in the future and further explore the layers of our Sun.

Next, Loren Matilsky (University of Colorado) presented the results of some heavy computer lifting. Since we can’t dive into the Sun and measure its magnetic fields, he reasonably points out, we have to make do with the next best thing: detailed computational models. Matilsky and his advisor Juri Toomre ran a massively parallel, fully 3D computer simulation of the Sun’s magnetic field evolution to understand what’s going on beneath the Sun’s surface and how that might drive the observed 11-year solar cycle. They found that a magnetic dynamo is generated to the north and south of the equator, migrates toward the equator, and is then reset — following the same pattern that we observe in sunspots. But in addition to this expected churning, Matilsky and Toomre found odder behavior: a wreath of magnetic field wandered back and forth between hemispheres, occasionally reversing polarity on a much longer cycle than the normal 11-year solar cycle. Is this a fluke of the simulation, or could this actually be representative of the behavior of magnetic fields beneath the Sun’s surface? Matilsky and Toomre aren’t sure yet, but they do note that the timing and behavior of this wandering dynamo is consistent with past observations that sometimes show heavier clustering of sunspots in one hemisphere for a while, and then in the other. Press release

Model of the structure of a buckyball. [Mstroek]

Can you spot the differences between the observations of the stellar stream GD-1 (top) and an unperturbed model (bottom)? Something massive appears to have passed through this stream, generating the gap and the small spur of stars.

The last speaker of the conference took us even further away, to the outskirts of the galaxy. There, stellar streams orbit within the Milky Way’s halo — and Ana Bonaca (Center for Astrophysics) and collaborators think these streams might reveal clues about the nature of dark matter. Stellar streams are thought to be created when stellar clusters in our halo are disrupted, drawing out long tails of stars that then orbit the Milky Way. The longer the tail, the longer the stream has likely been in existence. Bonaca reported on a study of one particular long stream of stars, GD-1, which she and collaborators analyzed in detail using data from PanSTARRS and Gaia. The team found that, upon closer inspection, the stream isn’t the smooth, continuous line of stars it appears to be. Instead, it has been perturbed: there are gaps and a small spur of stars mid-stream. Based on the team’s models, the most likely perturber was a compact object of around 5 million solar masses — yet such a perturber is nowhere to be seen. Could this perturber be a contributor to dark matter? Bonaca and collaborators plan to examine more streams to see if GD-1 is a fluke or a sign of more to come. If other streams show similar perturbations, we may be able to use these tracers to home in on dark matter models and explain where the invisible 90% of our galaxy is hiding.

Plenary Talk: Sexual Harassment – Changing the System (by Susanna Kohler)

In a replacement talk for the planned plenary — which Betsy Mills was unfortunately unable to give today — AAS Vice President Joan Schmelz (Universities Space Research Association) provided insightful and much-needed insights into how we can help change the system that allows sexual harassment to occur in astronomy.

In the wake of three very public sexual harassment cases in the field, Schmelz wondered what could be done to shift the burden from the vulnerable to the powerful members of the astronomy community. Since then, she has worked in her role as the former chair of the Committee for the Status of Women in Astronomy to identify ways we can shift the culture of the field.

Each of us falls somewhere on the advocacy axis. We can start by trying to do one step better.

Schmelz has since delivered talks at numerous institutions discussing ways that bystanders can move toward becoming allies and advocates. Her first recommendation is simple: each of us can start by moving one step up in the advocacy axis (see her slide at right). That means that if we’ve been the person telling sexist jokes, we should stop doing that. If we’ve been the person laughing at the jokes, we should stop laughing. If we’ve been a silent bystander before, next time we should speak up. Simple words such as “I disagree,” can shut down offensive conversation effectively. And, as with anything, practice makes perfect! Speaking up may not be easy at first, but it becomes easier with practice.

Schmelz addressed actions that can be taken at increasingly higher levels of leadership within an institution to change the culture around sexual harassment in the field. One interesting point she brought up is that faculty at many universities are mandatory reporters: they are legally required to (non-anonymously!) report cases of sexual harassment to the Title IX office or another campus authority. The Title IX office isn’t there to protect you, it’s there to protect the university, Schmelz points out. She argues that departments need to clearly present information like who is a mandatory reporter, and where targets of harassment can go on campus to receive guidance while keeping their identity anonymous.

Just a few of the many reasons why targets of harassment may not file a report.

The final topic Schmelz addressed is that of serial harassers. Targets of harassment are often — understandably — unwilling to report, fearing a he-said, she-said scenario. But what if it’s he-said, she-said, she-said, she-said? In the fluid environment of academia where people frequently move between institutions, the target of a serial harasser may have no idea that their experience wasn’t unique. An information escrow addresses this problem.

In an information escrow, an individual can file a report that will remain confidential unless and until a second report is filed against the same harasser. At that time, both filers are notified and can make the decision of how to proceed — whether they wish to have contact with one another, file a Title IX complaint, wait for a third case, or pursue another course of action. Schmelz pointed out that such an information escrow would be most effective if managed by the astronomy community as a whole, so that records remain intact as individuals move between institutions. She welcomed the community to take collective action to make such an escrow happen.

It’s clear that the astronomy community as a whole benefits when everyone is able to work to the best of their potential in a positive department climate. So why wouldn’t we all come together to change the system? It’s time that we each do our part.

Town Hall: The National Academies of Sciences: The Astronomy and Astrophysics Decadal Survey: 2020 (by Susanna Kohler)

They promised that we’d have town halls as part of Astro 2020, and here we are! The Astro 2020 Decadal Survey is a process during which the astronomy community assesses the current state of the profession and makes recommendations for what missions and projects should be prioritized over the coming decade. This evening Robert Kennicutt, co-chair of the Astro 2020 survey committee, presented an update on the current state of the survey.

The Astro2020 Decadal Survey is underway. [National Academies]

Where are we currently in the process? White papers have been solicited from the community, the survey committee has been selected, and the committee is currently building topical panels to review white papers and advise the survey committee. Panel deliberations will be conducted in late 2019, and survey-committee deliberations and report-writing will occur in spring and summer 2020.

We’re early in the game yet, but so far it looks like community involvement is high! As an example, the number of received science white papers is up by ~75% compared to the previous decadal survey, reports Kennicutt. The call for Activities, Projects, or State of the Profession Consideration white papers will be open for another month, and after that time the community can look for a few more town halls — including one at the winter AAS meeting in Honolulu, HI — as a means of keeping up to date with Astro 2020.

Editor’s Note: This week we’re at the 234th AAS Meeting in St. Louis, MO. Astrobites and AAS Nova will be working together to publish updates on selected events at the meeting this week; the usual posting schedule for AAS Nova will resume next week.

Kavli Foundation Lecture: Key Outstanding Questions in Galaxy Formation and How to Answer Them (by Kerry Hensley)

Dr. Alice Shapley (UCLA) kicked off the 234th meeting of the AAS with a discussion of some big open questions in galaxy formation and how we can work toward answering them. The biggest overarching question in the study of galaxy evolution is how the tiny density fluctuations in the early universe, long before galaxies formed and the first stars began to shine, resulted in the incredible diversity of galaxies we see in the universe today. She broke that question down into six smaller questions:

1. What physical processes drive the formation of stars in individual galaxies?
2. Why do galaxies today seem to fall into one of two categories: blue star-forming disks and “red and dead” spheroids?
3. How does matter assemble to form galaxies? Is it mostly in situ star formation or does a lot of the material and structure come from galaxy mergers?
4. Why is galaxy formation so inefficient?
5. How do galaxies exchange chemically enriched material with the intergalactic medium?
6. How do galactic stellar populations and central black holes co-evolve?

An (extremely blurry) example of how we can piece together a picture of how a single galaxy has evolved by observing similar galaxies at different points in cosmic time.

Dr. Shapley focused on galaxies with redshift between 1.5 and 3.5, since there was a lot going on in this time period: between a redshift of 2 and 3 was cosmic “high noon,” when the star-formation rate was at its maximum, and, coincidentally, the central black hole accretion rate was at a maximum as well. Observations show that galaxies at z~2 have more than an order of magnitude more star formation than galaxies today, are smaller (for a given mass), and have lots of gas inflows and outflows.

In order to study galaxies at these redshifts, Dr. Shapley uses optical spectroscopy. We can learn a lot from spectral lines: measuring the dust extinction, instantaneous star-forming rate, abundance of oxygen and other “metals”, and electron density, as well as determining whether the dominant ionization source is an active galactic nucleus or high-mass stars, and what kind of outflows are happening.

Of particular importance is the abundance of oxygen. If we measure the oxygen abundance in galaxies over the course of cosmic history, we can understand how galaxies become chemically enriched through stellar evolution and inflows, and chemically depleted through outflows.

Want to learn more about Dr. Shapley and her work? Check out her interview with Mia de los Reyes here!

Press Conference: Exoplanets, Flare Stars, and a Crab (by Susanna Kohler)

The first press conference of AAS 234 was a fun hodgepodge of topics, from exciting planet detections and updates on habitability to intriguing news about Sun-like stars.

In the first presentation, Lisa Prato (Lowell Observatory) and Christopher Johns-Krull (Rice University) jointly presented on the direct detection of CI Tau b, the youngest hot Jupiter to ever be observed directly. Hot Jupiters — gas-giant planets that orbit extremely close to their host stars — pose a particular challenge to detection: because they are so near to their stars, it’s quite difficult to separate the planet’s signal from its host’s, which is often hundreds of times brighter. But by combining 4 years of near-infrared spectroscopic observations of the CI Tau system, Johns-Krull, Prato, and collaborators were able to disentangle the carbon monoxide spectral lines of the planet CI Tau b from it’s star’s lines. This success is remarkable in such a young system; CI Tau is only around 2 million years old, and the star is still surrounded by the circumstellar disk of dust from which its planets formed. The system’s young age means that these observations of CI Tau b can provide unique constraints on models of how hot Jupiters like this one form — a long-standing question in exoplanet studies. Press release

Plot showing the narrowing of the habitable zone as a result of Schwieterman and collaborators’ work. The shaded region is the traditional habitable zone; blue indicates the part of this region that could support complex life. Click to enlarge. [Schwieterman et al. 2019]

Artist’s depiction of a planet orbiting a flaring star. [NASA, ESA and D. Player]

Helen B. Warner Prize Lecture: Hunting for Dark Matter in the Early Universe (by Kerry Hensley)

Dr. Yacine Ali-Haïmoud (New York University) began his talk with an overview of dark matter. Dark matter doesn’t seem to emit, scatter, or absorb light, but does interact with luminous (aka “normal”) matter gravitationally. Dark matter clumps together and forms the filamentary structure along which galaxies form. Astronomers infer the presence of dark matter in our observations of large-scale structures like galaxy clusters as well as small-scale structures like dwarf galaxies, and it turns out there’s a lot of it — it’s more than five times more common than normal matter.

But what is dark matter? Well, that’s the million-dollar question! Dr. Ali-Haïmoud outlined a few options:

• A new kind of particle. We’ve already discovered a whole host of particles, but there’s plenty of parameter space left unexplored. If it turns out that dark matter isn’t completely “dark” — that is, that it interacts very, very weakly with photons — there’s a chance that we could detect it with any of the many ongoing or planned experiments like CDMS, EDELWEISS, or ZEPLIN.
• Macroscopic objects that are hard to detect. The frontrunners here are primordial black holes, which are thought to form within microseconds of the Big Bang when dense patches of the universe collapse directly into black holes.
• A combination of the two. There’s no reason that the “missing matter” has to come from just one source!
• Not a physical object at all. Instead, dark matter could be a modification of the laws of gravity that only shows up under certain conditions.

A map of the anisotropies (temperature fluctuations) in the CMB from Planck.

We can try to figure out what dark matter is made of by studying the very early universe through observations of tiny temperature fluctuations in the cosmic microwave background (CMB). The CMB radiation almost perfectly matches that of a blackbody with a temperature of 2.73 K, but it has tiny fluctuations — called anisotropies — smaller than one part in 10,000.

These anisotropies are sensitive to the nature of dark matter. For example, if dark matter is made up of primordial black holes, the photons generated when matter falling into those black holes heats up (similar to the emission we see from active galactic nuclei) could ionize the surrounding hydrogen, which would have an effect on the ionization history of the universe. This change would be imprinted upon the anisotropies in the CMB.

The power spectrum of the CMB is very sensitive to the ionization history of hydrogen and helium. This figure shows how the power spectrum changes if you add in a little extra ionization in the past.

Observations of the CMB indicate that primordial black holes can’t be the only source for dark matter if they have masses greater than 100 solar masses. The potential range of primordial black hole masses is huge, though — anywhere from 10^-16 to 10¹⁰ solar masses. Twenty-six orders of magnitude! As far as our prospects of detecting these primordial black holes go, we have a chance of spotting them with the Laser Interferometer Gravitational-wave Observatory (LIGO) if they form in the correct mass range (a few to a few hundred solar masses) and form binaries. It’s still not clear whether or not these binaries, which would have formed very early in the universe’s history, would be able to survive the formation of large-scale structure in the universe. Clearly, there are lots of interesting questions left to be answered in our search for dark matter!

Learn more about Dr. Ali-Haïmoud in his interview with Kate Storey-Fisher here.

Press Conference: What’s New Under the Sun (by Susanna Kohler)

Though it’s been studied for centuries, our nearest star still poses a number of unsolved mysteries. This afternoon’s press conference introduced us to recent work addressing just a few of the open questions about the Sun.

Think the best images of our star all come from well-established, orbiting space telescopes? Think again! The High resolution Coronal Imager (Hi-C) is a telescope that was briefly launched to sub-orbital space on a sounding rocket; on each flight, it captured only a few minutes of observations of an active region of the Sun before returning to the ground. In that brief time, however, Hi-C took images with spectacular spatial and temporal resolution; just look at the video below (originally published on the Hi-C website) for a comparison of data from the orbiting Solar Dynamics Observatory AIA instrument to Hi-C observations!

In the first presentation of this press conference, Sanjiv Tiwari (Lockheed Martin Solar & Astrophysics Laboratory) presented discoveries made from data gathered during Hi-C’s second launch, just last year. The imager’s high-resolution observations revealed several different types of energy release — dot-like, loop-like, and jet-like brightenings — occurring on very small scales (perhaps a tenth of the diameter of Earth) within the core of an active region on the Sun. These energy releases appear to occur in the lower solar atmosphere in response to changes in the magnetic field on the Sun’s surface.

The small bright spots in this SDO image of the Sun represent coronal bright points, short-lived analogs of active regions. [NASA/SDO]

Can we make any predictions about solar activity? According to Alexander G. Kosovichev (New Jersey Institute of Technology), the answer is yes. Kosovichev reported on how helioseismology — the study of oscillations on the Sun’s surface — has given us clues as to the origin of the 11-year solar activity cycle. By using helioseismology to map zonal flows in the Sun, Kosovichev and collaborators found that hydromagnetic waves are generated at the bottom of the solar convection zone (that’s 120,000 miles below the Sun’s surface) and at about 60° latitude. These waves slowly travel to the surface and toward the Sun’s equator, eventually regulating the appearance of sunspots — but they are slowed by magnetic fields. This connection, Kosovichev argues, allows us to use observations of polar magnetic field strength to predict the strength of the next solar maximum. Based on the currently observed polar magnetic fields, Kosovichev and collaborators expect that the next solar maximum will be even weaker than the solar maximum of our current solar activity cycle.

The benefits of helioseismology as a tool for studying the Sun are clear, but the data products of this study can be difficult to intuitively understand. A new tool called Sonification of Solar Harmonics (SoSH, for short) is now helping to make helioseismology a little more accessible. The Sun’s surface oscillates because plasma flows excite sound waves that then bounce around the Sun’s interior; the star is effectively a giant resonant cavity for low-frequency sound waves. In helioseismology, we measure these waves to learn about the solar interior, but we don’t actually listen to the sound waves themselves … that is, until now. Solar physicist Timothy Larson (Moberly Area Community College) worked with composer collaborators to develop the SoSH project, in which helioseismology data is filtered and frequency-shifted into a hearable range. So far, SoSH has sonified two full solar cycles of data from two instruments (MDI and HMI on the Solar Dynamics Observatory), and these sonifications are publicly available so that everyone can listen to the surface of the Sun sing. More information and sample sonifications are located here.

Examples of different oscillation modes on the Sun’s surface. [SoSH]

George Ellery Hale Prize Lecture: Observations about Observations of the Sun (by Kerry Hensley)

WSO has amassed an amazing amount of data over the past 44 years!

Dr. Philip Scherrer (Stanford University) gave a broad overview of advances in solar physics over the past four decades through the eyes of three observatories: the Wilcox Solar Observatory, ESA/NASA’s Solar and Heliospheric Observatory, and NASA’s Solar Dynamics Observatory. Those three observatories have contributed to thousands of research papers with more than 4,600 unique authors and 40 PhD theses!

The Wilcox Solar Observatory (WSO), a ground-based solar telescope, has been observing the Sun since 1975. The WSO is responsible for the longest-running set of measurements of the Sun’s mean magnetic field as well as low-resolution magnetograms, both of which are used to study and predict the solar activity cycle. WSO has been observing the Sun for four full sunspot cycles! (Or two 22-year magnetic cycles. Your choice.)

A list of all the cool science MDI was designed to do.

Next came the Solar and Heliospheric Observatory (SOHO), which was launched in 1995. While SOHO is still alive and well, the Michelson Doppler Imager (MDI), which was used to make measurements of the Sun’s magnetic field, hasn’t been used for science since 2011. SOHO/MDI brought about huge advances in the field of helioseismology — a method of studying the interior of the Sun through observations of waves on its surface — including allowing scientists to “look” through the Sun to “see” sunspots on the other side!

Comparison of observations by WSO, MDI (SOHO), and HMI (SDO).

Finally, Dr. Scherrer showed some fantastic data and videos from Solar Dynamics Observatory (SDO), which was launched in 2010 and is still happily taking data from its vantage point in Earth orbit. One of SDO’s three instruments is the Heliospheric and Magnetic Imager (HMI), which makes measurements of the magnetic field of the Sun’s disk all at once. SDO has helped us better understand the large-scale motions of material within the Sun.

Throughout the talk, Dr. Scherrer shared some of his advice and lessons learned from his career. He shared his story of retracting a Nature paper claiming the discovery of the ever-elusive solar g-mode oscillations, which highlighted the importance of open discussion with collaborators and others, not rushing to publish science you aren’t confident in, and — perhaps most importantly — being mindful of your systematic errors!

Want to know more? Read his interview with Briley Lewis here.