New Map Locates Metals in Millions of Milky Way Stars

The new metallicity map, shown as the colored inset, indicates that the disk is composed of high-metallicity stars that typically are just a few billion years old (red and yellow shades). The disk is embedded in a low-density stellar halo composed of lower-metallicity stars with ages over 10 billion years (blue shades). The Milky Way is still growing by cannibalizing other nearby galaxies. A good example of a victimized galaxy is the Monoceros stream, marked by the arrow. The fact that the Monoceros stream stars have somewhat different metal content than other nearby stars (green shade instead of blue) helps to delineate its extent and reveal its origins. Credit: Zeljko Ivezic, University of Washington, SDSS-II Collaboration