The 232nd Meeting of the American Astronomical Society: Day 2

Posted by Jake Parks
on Wednesday, June 6, 2018

Welcome back! Today was the second full day of pure astronomical bliss here at the American Astronomical Society’s summer meeting. Yet again, the day was bursting with exciting presentations, exhibits, and conferences, so let’s dive right in with some highlights.

This afternoon, scores of local middle- and high-school students got hands-on access to the interactive exhibits and booths that are part of AAS summer meeting. Credit: Jake Parks
Creating the cosmos in a lab

To kick off the day, I sipped my morning coffee while attending the Laboratory Astrophysics Division’s Plenary Lecture: Small Interstellar Molecules and What They Tell Us. The lecture, given by David Neufeld of Johns Hopkins University, didn’t just describe our current understanding of the tiny particles of gas and dust that permeate the space between stars, but also stressed the importance of laboratory experiments in astrophysical research.

According to Neufeld (and backed up by plenty of studies), cooler regions of the interstellar medium (ISM) naturally form many different types of molecules. “In the last 80 years,” he said, “almost 200 distinct molecules have been detected in the interstellar medium.” Furthermore, observations of the ISM have shown that it is quite adept at taking simple molecules and forming more complex ones. Because the environment is not very intense (relatively speaking) in cooler regions of the ISM, Neufeld said that many of these molecules can be synthesized in the lab under the same conditions.

Neufeld also made sure to note that the ESA’s Herschel Space Observatory (thanks to HIFI, its high-resolution spectrometer) has discovered more than a half-dozen smaller molecules in the diffuse ISM, many of them hydrides – a compound made of a hydrogen atom and metal atom. One such compound was “Argonium,” the first noble gas molecule ever detected in space. Though Herschel has completed its mission, the Atacama Large Millimeter/submillimeter Array (with its vastly improved sensitivity) will continue searching for more hydrides at greater distances.

[Interesting side note: According to Neufeld, the highest energy cosmic ray ever measured was a single proton with 50 joules of energy. This is about as much energy as a decently thrown fastball.]

Stars that make you say WTF?

A bit later in the day, I headed to the press conference: Stars that Make You Say WTF (Where’s the Flux?), which addressed three studies focused on two very peculiar stars. The first two talks concentrated on the well-known Tabby’s Star (or Boyajian’s star) – a very oddly behaving star that exhibits huge, unprecedented dips in brightness.

The first of the Tabby’s Star talks was given by Yao Yin and Alejandro Wilcox, both from the Thacher School – a high school in Ojai, California. The two young researchers gathered their own data on Tabby’s Star and found evidence of chromatic dimming, which is where different colors of starlight are preferentially blocked by intervening gas and dust. Based on their data, the two suggest that the bizarre behavior of Tabby’s Star is due to multiple sources of light-blocking material.

In the next Tabby talk, Eva Bodman of Arizona State University presented research supported by a Kickstarter campaign (where backers were encouraged to choose names for the sporadic dips seen in the stars light curve). According to Bodman’s research, the dust cloud blocking light from Tabby’s Star is extremely complex, but we are likely just seeing different parts of the cloud at different times.

The final talk in this session was not related to Tabby’s Star, but instead focused on Epsilon Aurigae – the brightest member of a new class of “disk-eclipsed” binary stars. Presented by Robert Stencel of the University of Denver, this talk described a long-known variable star that exhibits its weirdness just once every 27 years. For this strange star, there has been a debate raging since 1929 concerning its mass. Is it 15 solar masses like some studies suggest? Or is it just a few solar masses like others have found? Well, according to Stencel, based on new Gaia data, the star is actually a relatively low-mass star in the giant phase of its life that has a blue main-sequence star hiding within its disk.

Gurtina Besla (right) from the University of Arizona gave an extremely captivating talk today that showed just how far our understanding of the Local Group has come in a few short years.
Probing galaxies with Gaia

Following the press conference, I attended the Plenary Lecture: The Dynamics of the Local Group in the Era of Precision Astrometry, which was brilliantly presented by Gurtina Besla from the University of Arizona. Besla, whose introduction included an impressive laundry list of accolades (especially for someone so young), did not disappoint. Although it’s only the second full day of sessions, this was by far the most engaging and compelling talk I’ve heard yet. In it, Besla explained (with the help of many beautiful images and animations) how over the past 10 years, new precise measurements of the motions of nearby galaxies have completely changed our understanding of how the Local Group is moving.

Specifically, Besla described how Gaia’s recent second data release not only clocked the speed of every galaxy within 100 kiloparsecs (330,000 light-years), but also provided the astronomical community with incredibly valuable motions for our neighboring galaxies in 6D phase space. (Gathering 6D phase space information means determining both the position and speed of an object in all three spatial dimensions.) With the new Gaia data, researchers can even determine the motions of individual stars within some bordering galaxies, which tells us how they are revolving.

Using these very, very accurate Gaia-determined motions, Besla explained how we can also rewind the tape on the movement history of nearby galaxies (such as the Large Magellanic Cloud). By doing this, Besla determined that the LMC is likely within about 50 million years of its first pass of the Milky Way. And if not, then it’s orbiting our galaxy with an extremely long-period orbit of about 5 billion years. Although this 6D phase space data is a fresh treasure-trove for astronomers to mine, it will still take a while to fully tap its potential. According to Besla, we are basically just realizing that Local Group dynamics are still not very well understood, so there is plenty more to come.

Until next time

As was the case yesterday, there was just far too much that happened today to do it all justice in just one short blog post, so stay tuned for more tomorrow. And don’t forget to keep checking in over the next few weeks as we continue to report on the most exciting science presented at the 232nd Meeting of the American Astronomical Society.


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