I’d just like to summarize some of the exciting new scientific results presented at the American Astronomical Society meeting in Seattle last month. I think it will be interesting to those of you science lovers who’re wondering what all the hubbub was about and for you astronomers who weren’t able to make it.
This is my third and final post in a series about the AAS meeting. The first two dealt with science policy, and diversity and sustainability. As I mentioned in a previous post, I enjoyed attending as both a scientist and science writer, and I was happy to personally meet the journalists writing excellent stories about the meeting (some of which I’ve linked to below).
I’ll start with some special sessions and other sessions focused on interesting science that included results I hadn’t seen before, and then I’ll end with some interesting plenary talks given by great speakers. It was a busy meeting and many of the sessions ran in parallel, so it’s inevitable that I missed some things and that this summary is incomplete. (Plus, I’m usually drawn to the sessions about galaxies, dark matter, and cosmology, and I often miss the other ones.) If you know of interesting announcements or talks that I missed here, you’re welcome to comment on them below.
Sloan Digital Sky Survey (SDSS)
After 15 years of great science, it was exciting to see the SDSS have its final public data release—until SDSS-IV data eventually come out, that is. At the press conference, Michael Wood-Vasey gave an overview, Constance Rockosi spoke about the data release, Daniel Eisenstein spoke about the Baryon Oscillation Spectroscopic Survey (BOSS), Jian Ge spoke about the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS), and Steven Majewski spoke about the APO Galactic Evolution Experiment (APOGEE). According to Rockosi, more than 6,000 papers have been published using publicly released SDSS data. The SDSS has observed tens of thousands of stars, hundreds of thousands of quasars, and millions of galaxies.
In addition, members of the BOSS collaboration presented (nearly) final results at a session dedicated to the survey. If you’re interested, check out this article I wrote about it for Universe Today. (Thanks to Nancy Atkinson for editing assistance.)
Distribution of galaxies in a slice of the BOSS survey. (Courtesy: SDSS-III)
Researchers presented newly published results and interesting work-in-progress about the evolution of distant galaxies using spectroscopic data from the 3D-HST survey, which is led by Pieter van Dokkum (Yale Univ.) and Ivelina Momcheva (Carnegie Observatories), combined with imaging data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), taking advantage of instruments aboard the Hubble Space Telescope. The figure below shows the spectral features of tens of thousands of galaxies, which indicate star formation activity, active galactic nuclei activity, and stellar age. If you’re interested, I wrote an article about some of these results for Sky & Telescope. (Thanks to Monica Young for editing assistance.)
Spectral features of high-redshift galaxies. (Courtesy: Gabriel Brammer, 3D-HST)
In a session dedicated to Andromeda—known as M31 by astronomers—as well as in other related sessions, research scientists and Ph.D. students presented studies about the stars, globular clusters, molecular clouds, dust, structure, dynamics, surface brightness profile, and stellar halo of the galaxy. The continued interest in our fascinating neighbor is understandable; Andromeda’s only 2.5 million light-years away from our galaxy! Like our Milky Way, Andromeda is a spiral galaxy, and it’s the most massive galaxy in the Local Group.
Many of these AAS results came from the Panchromatic Hubble Andromeda Treasury (PHAT) Survey, which is led by Julianne Dalcanton (Univ. of Washington), who presented highlights in a press conference as well. Dalcanton and her colleagues released this PHAT panoramic image of the galaxy below, and it received well-deserved press attention, including in NBC and Sky & Telescope.
Map of Andromeda galaxy. (Courtesy: HST, PHAT)
Many people were understandably excited about extra-solar planets, or exoplanets, detected by scientists with NASA’s Kepler space telescope. Every day of the meeting included talks and posters about the masses, abundances, dynamics, compositions and other properties of exoplanets as well as those of stars and supernova remnants examined with Kepler. In addition, astronomers’ announcement that they now have more than 1,000 confirmed exoplanets with Kepler and follow-up observations garnered considerable media attention (including these articles in Nature, BBC, and New York Times). They have at least 3,000 more planet candidates, and they will surely identify many more as Kepler continues its mission through 2016.
Of course, astronomers seek to find as many as possible Earth-like planets in or near the habitable regions orbiting Sun-like stars (often referred to as the “Goldilocks” zone). When these are successfully identified, the next step is to characterize their properties and try to assess the likelihood of life forming on them. Astronomers have found at least eight Earth-size planets in the habitable zone, including two of the newly announced ones, Kepler-438b and Kepler-442b. They also released these cool old-school travel posters. If you have a space ship that can travel 500 light-years a reasonable time, you should check out 186f on your next vacation!
Kepler’s alien planet travel posters. (Courtesy: NASA)
“Pillars of Creation”
On the 25th anniversary of the launch of the Hubble Space Telescope, astronomers released new images of the iconic star-forming region in the Eagle Nebula in the Serpens Cauda constellation, known as the “pillars of creation.” Journalists at Slate, CBS, and elsewhere shared these amazing images. At first I thought not much science was done with them, but by combining observations at visible and infrared wavelengths, astronomers can investigate what’s happening with the cold gas clouds and dust grains and assess how rapidly new stars are forming and where. For more, you can also see Hubble’s press release, which coincided with the press conference on the first day of the meeting.
Image of “pillars of creation.” (Courtesy: NASA and ESA)
I saw many other interesting talks and posters at the meeting, but I don’t have the time/space to get into them here. On galaxies and the large-scale structure of the universe (which I’m interested in), I saw talks involving modeling and measurements with the Galaxy And Mass Assembly (GAMA) survey, the Six-degree Field Galaxy Survey (6dF), and I presented research using the PRIsm MUlti-object Survey (PRIMUS). But the SDSS dominated the field.
In addition, Joss Bland-Hawthorn, Sarah Martell, and Dan Zucker presented some impressive early science results from the GALactic Archaeology with HERMES (GALAH) survey of the Milky Way, which uses an instrument with the Anglo-Australian Telescope. (GALAH is named after an Australian bird.) Astronomers combine GALAH observations with astrometry from Gaia and over the survey’s duration will produce detailed data for 1 million stars in our galaxy! In particular, they utilize a technique called “chemical tagging” to study the abundances of at least 15 chemical elements for each star, allowing for studies of stellar dynamics and merger events from infalling “satellite” galaxies. I look forward to seeing more results as they continue to take data and analyze them; their first public data release is planned for 2016.
I’ll briefly describe a couple of the plenary talks below, but I missed a few others that sounded like they could be interesting, including “The Discovery of High Energy Astrophysical Neutrinos” (Kara Hoffman); “Gaia – ESA’s Galactic Census Mission” (Gerry Gilmore); and “The Interactions of Exoplanets with their Parent Stars” (Katja Poppenhaeger).
Also, Paul Weissman (JPL/Caltech) gave an overview of the Rosetta mission and the comet C-G/67P, and Al Wootten (NRAO) gave an overview of many recent science papers using the Atacama Large Millimeter Array (ALMA). Rosetta and its lander Philae has run a few experiments already, and scientists with the mission have found that the bulk density of the nucleus is less than half the density of water ice and that its D/H ratio is different than the abundance ratio of the Earth’s oceans. More recently, Rosetta detected a crack in the “neck” of the comet, and they’ve abandoned an idea for a close flyby search for the lost lander, which might wake up in a few months when it receives more solar power. And if you’re interested in ALMA science, such as involving the gas kinematics of protostars and protoplanetary disks and the gas and dust clouds of distant galaxies, watch for proceedings from their recent Tokyo meeting, which are due to be published next month.
Cosmology Results from Planck
Martin White (UC Berkeley) gave an excellent talk about cosmological results from the Planck telescope, which he described as having the “weight of a heavy hippo and the height of a small giraffe.” Based on analyses of the power spectrum of the cosmic microwave background (CMB) radiation, so far it seems that the standard model of cold dark matter plus a cosmological constant (ΛCDM) is still a very good fit. Scientists in the collaboration are obtaining tighter constraints than before, and the universe still appears very flat (no curvature). They are planning a second data release this year, including more simulations to assess systematic uncertainties and more precise gravitational lensing measurements. White ended by saying, “I can explain to you what really well, but I can’t tell you why at all.”
White also hinted at, but didn’t reveal anything about, the joint analysis by Planck and BICEP2 astrophysicists. That analysis was completed recently, and now it seems that the detected polarization signal might be at best a mixture of primordial gravitational waves produced by inflation and of Milky Way dust, and they’ve obtained only an upper limit on the tensor-to-scalar ratio. Check out my recent article in Universe Today about this controversy.
Inflation and Parallel Universes
Max Tegmark (MIT) has talked and written about both inflation and the multiverse for many years, such as in a 2003 cover article and a recent blog post for Scientific American and in his book, “Our Mathematical Universe.” From the way he presented the talk, it was clear that he has discussed and debated these issues many times before.
Tegmark began by explaining models of inflation. According to inflation, the universe expanded for a brief period at an exponential rate 10-36 seconds after the Big Bang, and the theory could explain why the universe appears to have no overall curvature, why it approximately appears the same in all directions, and why it has structures of galaxies in it. In one entertaining slide, he even compared the expansion rate of a universe to that of a fetus and baby, but then he said, “if the baby kept expanding at that rate, you’d have a very unhappy mommy.”
Expansion rates of a baby (human) and a baby universe
He subtitled his talk, “Science or Science Fiction?”, and that question certainly came up. Tegmark argued that inflation seems to imply at least some levels of a multiverse (see his slide below), which makes many astrophysicists (including me) nervous and skeptical, partly because parallel universes aren’t exactly testable predictions. But he made the point that some general relativity predictions, such as about what happens in the center of a black hole, aren’t testable yet we accept that theory today. He discussed “modus ponens” arguments: once we accept “if p then q,” then if p is asserted, we must accept q, whether we like it or not. In other words, if inflation generally predicts parallel universes and if we accept inflationary theory, then we must accept its implications about parallel universes. This is an important issue, and it’s another reason why BICEP2 and Planck scientists are trying to resolve the controversy about polarization in the CMB.
Predictions of different levels of the multiverse.
The Dark and Light Side of Galaxy Formation
Finally, in another interesting talk, Piero Madau (UC Santa Cruz), who was recently awarded the Heineman Prize for Astrophysics, spoke about galaxy formation and dark matter. In particular, he spoke about difficulties and problems astrophysicists have encountered while attempting to model and simulate galaxies forming while assuming a cold dark matter (CDM) universe. For example, he described: the cusp-core controversy about the inner profiles of dark matter clumps and galaxy groups; the problem of angular momentum, which is conserved by dark matter but not gas and stars; the missing satellites problem, in which more simulated dark matter subclumps (“subhaloes”) than observed satellite galaxies are found; and the “too-big-to-fail” problem, such that simulated subhaloes are much more dense than the galaxies we see around the Milky Way. These problems motivated astrophysicists to rethink assumptions about how galaxies form and to consider warm or self-interacting dark matter.
Madau ended by saying that evidence that the universe conforms to expectations of the CDM model is “compelling but not definitive,” and warm dark matter remains a possibility. Considering all of the exciting work being done in this field, this could be “the DM decade”…but then he said people have been talking of a DM decade for the past thirty years.