The 231st Meeting of the American Astronomical Society: Day 3

Posted by Alison Klesman
on Thursday, January 11, 2018

The galaxy SDSS J1354+1327, seen in the lower right corner of the image, has a central supermassive black hole that's let out two distinct burps in the past 100,000 years. The greenish cloud to the lower left is the 'old burp,' while the bright arc on the upper part of the galaxy is the 'new burp.' // Photo Credit: X-ray NASA/CXC/University of Colorado/J. Comerford et al.; Optical: NASA/STScI

Thursday morning at the AAS pulled space telescopes into the spotlight with a morning press conference highlighting the work our instruments in space have helped astronomers to complete. Keith Gendreau of NASA’s Goddard Space Flight Center spoke about the Neutron star Interior Composition Explorer (NICER) aboard the International Space station, and how its data is working to provide a completely independent method for navigating deep space using the pulses received from millisecond pulsars via the SEXTANT software. These astronomical objects spin so regularly that they can be used in lieu of atomic clocks and GPS positioning for both near-Earth orbit and missions throughout the solar system — and beyond. Pulsar navigation can provide either a failsafe for manned missions, or a go-to positioning option for spacecraft to improve positioning, regardless of distance from Earth.

Next up was Will Clarkson of the University of Michigan-Dearborn, who showed that the Hubble can be used to peer into the galactic center and chart the motions of stars based on their chemical composition. Clarkson and his colleagues are wondering whether stars of similar composition follow similar orbits — it turns out, they do — and want to know what that says about stellar evolution in the bulge of our galaxy and beyond. Their ultimate goal now is to use scenarios of stellar and galactic evolution to produce properties that can be tested using observations to help astronomers better pin down how our galaxy was built.

Julie Comerford of the University of Colorado, Boulder, shared a fascinating detection of a supermassive black hole inside a galaxy that has undergone two separate “burps,” as she called them, spewing out gas following a feast of dust and gas. These burps are not surprising, as models show that supermassive black holes should “flicker” like this — go through a cycle of feasting, burping, and napping — frequently. Comerford’s group found this to be true, with this particular black hole showing evidence of a burp 100,000 years ago, then a dormant period preceding the much more recent burp. This particular black hole’s activity is likely related to interaction with a nearby companion, but a companion is not necessary to spur these monster black holes’ feasts. Our own central supermassive black hole shows evidence of these burps as well, in the giant Fermi bubbles mentioned in my blog yesterday.

The morning’s press conference wrapped up with a presentation by Brett Salmon of Texas A&M University on the discovery of a distant galaxy just 400 million years after the Big Bang. This smudgy galaxy is nonetheless the most resolved galaxy astronomers have ever seen at this distance, measuring about 2,500 light-years across (about half the size of the Small Magellanic Cloud) and just 1/100th the mass of our Milky Way. Followup with the James Webb Space Telescope should allow astronomers to determine whether it is disk-dominated or still too young for a significant disk component to have formed. This particular time in the age of the universe, when it was just a few percent of its current age, marks what astronomers think should be the transition from chaos to order in galaxies.

This afternoon, we learned that the structure in a disk like this might not need planets to form. // Photo Credit: ALMA (ESO/NAOJ/NRAO), NSF

Thursday afternoon’s press conference switched tacks to focus on molecules, dust, disks, and planets. Brett McGuire announced that the Green Bank Telescope has found complex molecules in the Taurus Molecular Cloud; the successful detection of benzonitrile in this region of cold gas marks the largest molecule discovered via radio observations to date. This molecule can be used as a tracer for polycyclic aromatic molecules, which tie up about 10 percent of the universe’s carbons and can combine to ultimately form organic molecules.

Marc Kuchner then spoke about the beautiful and complex rings and spiral structures astronomers often see in planetary disks. These structures, which develop in the disks around young stars, are often believed to be an indication of planets forming within the disks. But, it turns out, no planets are needed to get these structures to arise — only an effect called photoelectric instability, which occurs as UV light from the young star hits dust grains in the disk, knocking off electrons and causing localized heating of the gas. This result comes from simulations performed with NASA supercomputers, following 400,000 particles embedded in gas and watching how they interacted with UV light over time. Kuchner stresses that this work doesn’t mean none of the structures we see in disks are due to planets, just that we can’t always assume the existence of planets inside a disk that shows these patterns.

A shot of the large Exhibit Hall here. // Photo Credit: Astronomy: Alison Klesman

Jessie Christiansen of Caltech shared details about the K2-138 system, a planetary system of at least five sub-Neptune-sized planets crammed in close to a star just a little smaller and cooler than the Sun. This system is unique in many ways, including the fact that it was the first multiple-planet system found by citizen scientists and it’s the first in which there is an unbroken chain of orbital resonances linking each planet. Each planet is in a nearly 3:2 resonance with the one beyond it, the largest chain of resonances like this found so far. A sixth planet candidate lies further along the chain; if confirmed, it not only continues the trend, but suggests there may be more undiscovered planets in the “gaps” in resonance between the last known planet and this new one. The system can now be used by astronomers to learn more about how planets migrate inward toward their star, as it’s clear the planets didn’t form where they sit today.

Finally, we heard from Giovanni Strampelli of the Space Telescope Science Institute, who spoke about the discovery of new stellar companions — some stars, some brown dwarfs, and some planets — around stars in the Orion Nebula Cluster. He discussed the challenges of finding companions using images of this region, and finally showed results that included some brown dwarf-brown dwarf pair, and a possible planet-planet pair (though, of course, just because an object falls within the planetary mass range, doesn’t mean it’s necessarily a planet).

One of the many posters presented at the meeting this year. This is work completed by a friend of mine to develop code to help identify transiting exoplanets. // Photo Credit: Astronomy: Alison Klesman

This was the last press conference of the meeting, as much of the press — myself included — will be heading offsite tomorrow to visit the Space Telescope Science Institute and learn more about the upcoming James Webb Space Telescope.

I spent the rest of my day threading my way through the booths and posters in the Exhibit Hall, which was much, much bigger than the one at the summer meeting. It’s been a busy meeting thus far, so I’m looking forward to a slightly slower day tomorrow, even if I’m pretty excited to visit STScI and learn more about JWST.

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