AAS 229: Day 4


Editor’s Note: This week we’re at the 229th AAS Meeting in Grapevine, TX. Along with a team of authors from astrobites.com, I will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com, or catch our live-tweeted updates from the @astrobites Twitter account. The usual posting schedule for AAS Nova will resume next week.

AAS Hack Day (by Joanna Bridge)

Today was the #AAS229 Hack Day! Hack Day, this year sponsored by Northrop Grumman, has occurred on the final day of AAS conferences for several years now. About 50 astronomers gathered together to combine their extensive brain power to work on projects pitched by various people in the room. These projects ranged from in-depth coding to sewing, the common thread being simply that we created.

A comprehensive list of the projects undertaken today will be found here as participants add their hacks to the site. If you want to follow the progress as it occurred, check out the Twitter hashtag #hackAAS. Here is a list of some of today’s accomplishments:

  • Composing letters to your politicians
  • Solving differential equations numerically using basis functions
  • Getting tests to work in astropy with a new version of pytest
  • Creating a repository of hacks from Hack Day for future reference
  • Overlaying K2 postage stamps with SDSS images
  • Building a database with literature on inclusivity for easy access
  • Planning and budgeting for the revitalizing of an unused planetarium at City College of New York
  • Saving PNG plots with metadata in python
  • Sewing extravaganza using cloth posters and other fabrics – bowties, infinity scarves, bibs, bags, hair accessories, and capes!

See the stream of the results on Periscope from this tweet:

Hack Day was a great success and I personally cannot wait for the next one!

Lancelot M. Berkeley Prize: Exploring for Galaxies in the First Billion Years with Hubble and Spitzer ‐ Pathfinding for JWST (by Ashley Villar)

Garth Illingworth kicked off the final day of #AAS229 with the Lancelot M. Berkeley Prize lecture on very, very old galaxies. He specifically studies the formation (or ‘build-up’) of these galaxies at very large redshifts of ~10 (just 500 million years after the big bang!) using telescopes like the Hubble Space Telescope (HST) and Spitzer.

Although these young galaxies are small (and often unresolved), large surveys have allowed Illingworth and others to better understand statistical properties of the early galactic populations as functions of time. As one example, the luminosity function of these galaxies (the number of galaxies as a function of brightness) becomes extremely steep at the faint end of galaxies. This luminosity function can be compared to a star formation history as a function of redshift. At large redshift, Illingworth points out that the luminosity seems to agree with the star formation histories, meaning that reddening from dust has a small effect at high redshifts.

Looking forward, Illingworth is excited about the next generation space missions, including JWST and WFIRST. Both will have the capacity to study the very earliest galaxies and the buildup of galaxies over the course of cosmic time. JWST launches in 2018, so exciting results are just around the corner!

Press Conference: Black Holes, Green Galaxies, Old Stars & NuSTARs (by Susanna Kohler)

The authors' model of what causes a moving shadow in TW Hydrae's disk. [NASA, ESA, and A. Feild (STScI)]

The authors’ model of what causes a moving shadow in TW Hydrae’s disk. [NASA, ESA, and A. Feild (STScI)]

The second-to-last press conference of the meeting was, as AAS Press Officer Rick Fienberg put it, an “astronomical potpourri” covering a discovery in a protoplanetary disk, nearby black holes, measurements of the Milky Way’s mass, and distant galaxies.

The first briefing was given by John H. Debes (Space Telescope Science Institute), who discussed how an old instrument on Hubble, the Space Telescope Imaging Spectrograph (STIS), was used to make a new discovery around a nearby star. Observations from STIS revealed an asymmetry rotating around the disk of gas and dust surrounding TW Hydrae, a stellar system located ~200 light-years away from us. The asymmetry had a 16-year rotation period, which is too fast for it to be a feature actually moving within the disk. Instead, astronomers have proposed that it is a shadow cast on the outer disk by a potentially misaligned inner-disk region. They calculate that the warping of the disk could have been caused by the presence of a Jupiter-mass planet orbiting in a gap at ~1 AU from the central star. For more information, check out the press release here.

Next up was a tag-team of Ady Annuar (Durham University, UK) and Peter Boorman (University of Southampton, UK), who presented on two nearby supermassive black holes that have been recently imaged directly for the first time. IC 3639 and NGC 1448 are galaxies located at 170 million and 38 million light-years away, respectively, and they both contain supermassive black holes at their cores. These black holes have remained undiscovered until recently, however, because they are heavily obscured by a surrounding torus of the gas and dust that feeds them. Because we are viewing these two galaxies edge-on, the obscuring torus prevents us from seeing the black holes. NASA’s X-ray telescope NuSTAR (Nuclear Spectroscopic Telescope Array), however, was able to examine these galaxies and identify the black holes feeding on material at their centers — and even provide more information about the gas and dust shrouding them. Read more in the press release here, and check out below an awesome animation that Boorman showed us: an artistic rendering of a torus rotating around a supermassive black hole. [Made by Ricardo Ramírez based on a publication led by Marko Stalevski]

green glow

NGC 6826, a planetary nebula, provides a striking example of the green glow created by emission from doubly ionized oxygen. [HST/NASA/ESA]

The third presentation, given by Gwendolyn Eadie (McMaster University), discussed recent efforts to measure the mass of our galaxy. One of the best ways to estimate how much mass the galaxy contains — including dark matter, which can’t be detected directly — is to measure the velocities of globular clusters bound to the galaxy (whose orbits are determined by the gravitational pull of the Milky Way). Unfortunately, our measurements of these velocities are incomplete: some proper motions of Milky Way globular clusters aren’t yet known. Eadie and collaborators have made clever use of Bayesian statistics to use the values we do know — as well as the uncertainties about those we don’t — to make new, more accurate estimates of our galaxy’s mass, finding that the Milky Way contains a mass of roughly 400–580 billion solar masses. More info can be found here.

The final briefing was given by Matthew Malkan (University of California, Los Angeles) on the subject of young galaxies in the early universe. A recent examination of thousands of distant galaxies in the Subaru Deep Field yielded the discovery that all small galaxies are very strong emitters of the green emission line of doubly-ionized oxygen. This emission is surprising, as only extremely energetic X-ray photons can cause this double ionization — and few such high-energy photons are produced by young stars in modern galaxies. Malkan postulates that the early generations of star formation we’re viewing in these distant, small galaxies produces much hotter stars. You can read more about the discovery in the press release hosted here.

Seminar for Science Writers: The August 2017 All-American Solar Eclipse (by Natasha Batalha)

The second press conference of the day covered the exciting science and the logistics of the August 21, 2017 total solar eclipse. The path of this eclipse sweeps across the entire United States, which is incredibly rare. Although total solar eclipses happen every year, they are usually only visible in non-populated areas such oceans or arctic regions. In fact, this marks the first eclipse to grace the continental U.S. since 1979 and the first to go coast-to-coast since 1918!

The first talk by Jay Pasachoff, from Williams College, covered some of the science that can be done during the eclipse. His group will study the dynamics of the solar corona and the frequency of oscillations as seen through special coronal filters. Many people are very surprised to hear how many questions about the Sun are still unanswered. For example, we still don’t fully understand why the corona is millions of degrees hotter than the surface of the Sun. We usually attribute it to the Sun’s magnetic field, but it’s not entirely clear how. The natural ability of the Moon to block out the Sun offers scientists an opportunity that would otherwise be very technologically complex. Given the cover photo image at the top of the page, it’s easy to see how!

Next up, Alex Young from NASA Goddard Space Flight Center explained the efforts that NASA and other large agencies will be providing. NASA’s goals during the total eclipse will be to engage and educate the public, as well as support all the work being done in the nation. NASA will also collaborate with the AAS and NSF to promote safety. Both NASA and AAS have websites with resources so you can start planning your August 21 vacation.

Michael Zeiler/ GreatAmericanEclipse.com

Michael Zeiler/ GreatAmericanEclipse.com

Although there is much to be excited about, Angela Speck from University of Missouri explained some of the challenges that we will encounter. First off, we need to start communicating to the public about how rare this event is. There are only 12 million people in the U.S. that don’t need to drive. But, Dr. Speck pointed out that 99% of the U.S. is within a long day’s drive to a total eclipse area. Major cities in the total eclipse zone, such as Nashville, have the potential to be wildly packed.

Lastly, AAS’s very own Rick Fienberg expanded on some of the eye safety facts the public should and should not be concerned with. A total solar eclipse is about as bright as the full moon and just as safe to look at (even with binoculars or a telescope). But during the partial eclipse times there is a genuine risk of retinal injury. However, there are still some pretty high misconceptions regarding this. Here are the major ideas you should communicate to your friends and family:

  1. Sunglasses cannot be worn in place certified solar viewing glasses
  2. Retinal injury is actually quite uncommon, although we do not advise any prolonged Sun-staring
  3. The Sun does not emit dangerous rays during a solar eclipse and the Moon does not have any focusing effects

This solar eclipse might be a once in a lifetime event, so start planning your trips now!

The 2017 Total Solar Eclipse: Through the Eyes of NASA (by Michael Zevin)

Start counting down the days until August 21, 2017. On this special day, we will have the first total solar eclipse to hit mainland U.S. in almost 40 years, and its band of totality will darken a 70-mile stretch of Earth all the way from Oregon to South Carolina. Today’s plenary talk by C. Alex Young, the Associate Director for Science at NASA Goddard Space Flight Center, ignited excitement in all the astronomers in the room for the upcoming astronomical phenomenon.

Young himself admitted that he has never seen a total solar eclipse. Surprisingly, he was far from alone. Even in a room full of astronomers, the vast majority conceded when asked who has never seen totality. However, starting with the eclipse in August, Young is “looking forward to becoming a total eclipse junky.” Young started by showing movies of previous solar eclipses, and the sheer awe and exhilaration that it induced on the lucky observers who documented the events. Young displayed a quote by David Baron, author of American Eclipse, who describes the experience perfectly: “For three glorious minutes, I felt transported to another planet, indeed to a higher plane of reality, as my consciousness departed the Earth and I gaped at an alien sky.”

The eclipse in August 2017 will cast a shadow about 70 miles wide and traverse from the Pacific to the Atlantic coastline in just about 1.5 hours. To get the longest view, I recommend renting a supersonic jet plane and following beneath the shadow at a blazing 2000 miles an hour. However, for most people that are forced to stay stationary, totality will last about 2 minutes.

Young showed some of the great visualizations that NASA has been producing for this eclipse, including a great animation showing how the solar energy impacting the Earth changes during the eclipse. Because of the blocked sunlight, the temperature is expected to rapidly drop 5-15 degrees during totality, which Young says will affect the wildlife, certain types of vegetation, and small scale weather.

Lastly, Young implored the astronomical community to take part in this historic event! By visiting eclipse2017.nasa.gov, one can see the path of totality (which traverses many national parks) and find the best places to view the eclipse. As astronomers, Young asked that we connect our science to the eclipse and take part in the many outreach efforts that will be underway. Exoplanet transits, coronal activity around AGN, and many more research topics can be connected to our Sun’s special day. Mark your calendars and buy your solar glasses so you can see the darkness on August 21st!

Plenary Session: How Supermassive Black Hole Feedback Might Work (Ashley Villar)

Megan Donahue finished up the conference with a fascinating talk on supermassive black hole feedback. We now believe that almost all galaxies have supermassive black holes in their centers. However, the relationship between the growth and activity of the black hole and its surrounding gas is still an active field of research. You might be wondering what gas we are talking about. When you imagine the anatomy of a spiral galaxy, you probably think of the flat disk and the central bulge, but there is also a huge amount of cold gas surrounding most galaxies which is known as its circumgalactic medium (CGM). This CGM contains most of the galaxy’s baryons and metals.

Active galactic nuclei (AGN), or active black holes in galaxies, interact with the CGM in such a way that, as Donahue puts it, the galaxy is “marginally stable to condensation.” In other words, the AGN will become active and overheat the CGM which decreases precipitation onto the AGN and cools the system. Once cooled, star formation increases and reheats the system, again activating the AGN. Donahue quantifies this cycle using the ratio between the so-called cooling time of the system and the free-fall time. Systems under this theoretical model generally have a ratio of 10:1 for cooling to free-fall times. This is seen in both simulations and real massive galaxies.

This simple theory also reproduces several well-known galactic relations with little to no fitting of free parameters. For example, the theory is able to reproduce the mass-metallicity relation (in which more massive galaxies tend to be more metal-rich), and the M-sigma relation (in which galaxies with larger supermassive black holes have more velocity dispersion in their bulge). While the exact mechanism by which this feedback occurs is uncertain, this new theory seems to at least begin to explain many complex relations we need between galaxies and their central black holes.