KISSIMMEE, FLORIDA—Astronomers have long predicted that the oldest stars in our Milky Way galaxy are in the center, while its outer environs are full of younger objects. Now, they have mapped out their prediction in exquisite detail, thanks to the Sloan Digital Sky Survey (SDSS), a 2.5-meter telescope at the Apache Point Observatory in Sunspot, New Mexico. A team of astronomers used SDSS to determine the masses of red giant stars, bright stars nearing the end of their lives, scattered throughout the Milky Way. The older a red giant, generally speaking, the lower its mass. But SDSS cannot measure mass directly. As the team described to the American Astronomical Society meeting here today, they combined the spectra of light from the red giants with data from NASA’s Kepler observatory, designed to find exoplanets, to calculate the masses of 70,000 red giants across a large swathe of the Milky Way, out to a distance of 50,000 light years. In the map, shown above, the focus with lines coming out of it is the location of Earth. To its right are older stars (red) around the galactic center and to its left are younger (blue) stars in the outer parts of the disk. As the team says, the Milky Way grew out as it grew up.
*Correction, 12 January, 3:47 p.m.: This item was updated to reflected that the stars studied were red giants, not red dwarfs.