Free Astronomy Magazine January-February 2016

SPACE CHRONICLES U sing NASA's Hubble Space Te- lescope to conduct a "cosmic archaeological dig" at the very heart of our Milky Way galaxy, as- tronomers have uncovered the blue- prints of our galaxy's early construc- tion phase. Peering deep into the Milky Way's crowded central hub of stars, Hub- ble researchers have uncovered for the first time a population of an- cient white dwarfs — smoldering remnants of once-vibrant stars that inhabited the core. Finding these rel- ics at last can yield clues to how our galaxy was built, long before Earth and our Sun formed. The observations are the deepest, most detailed study of the galaxy's foundational city structure — its vast central bulge that lies in the middle of a pancake-shaped disk of stars, where our solar system dwells. As with any archaeological relic, the white dwarfs contain the history of a bygone era. They contain infor- mation about the stars that exist- ed about 12 billion years ago that burned out to form the white dwarfs. As these dying embers of once-ra- diant stars cool, they serve as multi- Hubble uncovers fading cinders of some of our galaxy's earliest homesteaders by NASA N ASA's Hubble Space Tele- scope has detected for the first time a population of white dwarfs embedded in the hub of our Milky Way galaxy. The Hubble images are the deepest, most detail- ed study of the galaxy's cen- tral bulge of stars. The smoldering remnants of once-vibrant stars can yield clues to our galaxy's early construction stages that hap- pened long before Earth and our sun formed. [Left] — This is a ground-based view of the Milky Way’s central bulge, seen in the direction of the constellation Sagittarius. Giant dust clouds block most of the starlight coming from the galactic center. Hubble, however, peered through a region (marked by the arrow) called the Sagittarius Win- dow, which offers a keyhole view into the galaxy's hub. [Upper right] — This is a small section of Hubble's view of the dense collection of stars crammed together in the galactic bulge. The region surveyed is part of the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) field and is Hubble uncovered extremely faint and hot white dwarfs. This is a sample of 4 out of the 70 bright bulge. Astronomers picked them out based on their faintness, blue-white color, and motion relative spond to the white dwarfs' location in the larger Hubble view. [A. Fujii, NASA, ESA, A. Calamida