The Coldest Stars: Y Dwarfs and the Fuzzy Border Between Stars and Planets
Stars in our Milky Way Galaxy have a wide range of masses, sizes, surface temperatures and luminosities, but they all share one common feature: the ability to convert hydrogen into helium through nuclear fusion. These elemental foundries release tremendous amounts of energy, and seed the cosmos with the building blocks for planets and life. However, below a certain mass--around 7% of the Sun's mass--the interiors of stars fail to get hot enough to fuse hydrogen. These "failed stars" are called brown dwarfs, and their discovery in the mid-1990s fulfilled a decades-long prediction of the existence of an extensive "dark population" in our Galaxy. Today, thanks to advances in infrared detector technology, over 1000 brown dwarfs are known, adding three new letters to our spectral sequence of stars. In this talk, I will highlight the most recent additions, the Y dwarfs, a class of ultracold brown dwarfs whose atmospheres have the same temperatures and pressures (but not compositions) as the Earth. I will discuss the remarkable properties of these strange worlds, including the presence of clouds, weather and auroral emission, and explain why these sources may encompass the edge of star formation and ruffle the unsettled boundary separating stars from planets.
Dr. Adam Burgasser is an Associate Professor of Physics at UC San Diego, specializing in the observational investigation of the coldest stars, brown dwarfs and extrasolar planets. He is best known for discovering and establishing the T spectral class of brown dwarfs; he also investigates low-temperature stars in the Galaxy's halo population, low-mass multiple systems, and stellar magnetic activity at optical and radio wavelengths. In addition, Dr. Burgasser is examining ways of melding the tools of the two "useless professions" of art and astronomy, and is collaborating with faculty in Theatre and Visual Arts on a project called Project Planetaria. A native of Buffalo, NY, Dr. Burgasser fled the snow and attended UCSD as an undergraduate where he earned his Bachelor's in Physics, a minor in Theatre and Dance, and an NCAA national championship in springboard diving. He received his PhD in Physics in 2001 from the California Institute of Technology, and did postdoctoral work at UCLA and the American Museum of Natural History in New York City. In 2009 he moved back to UCSD following a faculty position in the MIT Department of Physics, where he left behind his beloved "Adam J. Burgasser Endowed Chair of Astrophysics". He lives in Encinitas, CA.
"What's Up?" in this month will be presented by John Garrett