Research

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Research

$Academic Vital Stats CV Publications Stellar Indigestion “Oh, you’re the guy who studies the burps before the throw-up!” — anonymous When describing my research, I like to use a particularly colorful analogy. Most people are familiar with the term supernova, which is what astronomers call the explosion of a star at the end of it’s life. In this violent event, a star that started its life weighing more than about 10 times the mass of the Sun expels a large fraction of its mass out into the cosmos. In the process, it seeds the universe with the very elements needed to make the Earth, the Moon, your eyes, and the screen into which they are currently gazing. If we think of this event as the star projectile vomiting, spewing its guts out into the universe, then what I study is something like a stellar burp. Carl Sagan famously said, “We are made of star stuff.” I might modify that last word. To be a bit more specific, I am currently working with Professor Eliot Quataert on an investigation of what is going on inside a star that makes it burp. We are attempting to diagnose stellar indigestion. Astronomers have known for decades that massive stars burp (the picture in the header is one particular brilliant example of the aftermath of a burp from Eta Carinae, one of the most massive stars known in our galaxy); they do so at various stages in their lives. Perhaps most interestingly, some burp in their final moments before exploding. If we were to put a massive star’s life on a human scale, compressing multiple millions of years down to, say, a hundred, then on that scale a rare few stars let out impressive belches just hours before their explosive deaths. And despite decades of observations, these events have thus far gone unexplained. Professor Quataert and I are approaching this problem by looking at the stability of processes taking place deep within a star’s interiors throughout its life. We produce theoretical models of stars with the excellent, open-source MESA stellar evolution code, and analyze their stability to various perturbations. Perhaps the most interesting idea we have come up with involves the vigorous nuclear burning and convective motions taking place deep within a massive star during its final stages of life. We have proposed an idea we term “wave-driven mass loss,” which may provide the best explanation for the giant eruptions observed within the year prior to a star exploding as a supernova (here’s a short talk I gave on the subject at a 2012 workshop on massive stars in Minnesota). For one particularly recent example, SN 2010mc, an independent analysis deemed our model the best fit to the observations (Nature news, journal article). Rare, oddly-named astronomical sources “So it’s called a ‘planetary nebula,’ but it has nothing to do with planets?” In the beginning of my career at UC Berkeley, I worked with Professor Josh Bloom attempting to identify new AM Canum Venaticorum (AM CVn) binary systems in the Stripe 82 survey conducted by the Sloan Digital Sky Survey. AM CVn are among of the closest-separated, shortest-period binary star systems known. They are also among the few systems in the universe for which changes in the binary’s orbit arise primarily due to the emission of gravitational waves, traveling ripples in the very fabric of the universe. They will be some of the most prevalent sources of gravitational waves for the coming generation of advanced gravitational wave detectors like LIGO. As an undergraduate at Boston University, I worked with Professor Dan Clemens on a variety of observational astronomy projects. The most substantial of these was a two-square-degree (a square about four moons wide and tall) imaging survey in search of planetary nebulae, the beautiful remnants left behind by evolved stars slightly more massive than the Sun. We completed the survey in 2007 as my senior thesis for distinction project at Boston University. We used a custom optical filter, to selectively observe only a narrow range of colors, and the 1.8-meter Perkins Telescope at Lowell Observatory in Flagstaff, AZ. Using this technique, we had hoped to isolate a particularly distinctive feature in the spectra of planetary nebulae.$ shapeimage_2_link_0