Space.com: To construct the map, scientists measured the composition and masses of red giant stars to determine their ages. by Nola Taylor Redd
'"This is key to understanding galaxy formation," Melissa Ness, a postdoctoral student at the Max Planck Institute for Astronomy in Germany, said. Ness lead a group that used the Sloan Digital Sky Survey (SDSS) to study the light, or spectra, from red giant stars to produce the first global age map of the Milky Way. "Measuring the individual ages of stars from their spectra and combining them with chemical information offers the most powerful constraints in the galaxy," she said.
'"This is somewhat revolutionary, because ages have previously been considered very hard to get," Ness said. With this age map, the scientists were able to chart how the Milky Way has grown throughout its lifetime. They found that the more-ancient, 13-billion-year-old stars were the first to form early in the lifetime of the universe. As the young galaxy collected gas and dust in a growing disk around its edges, the material became the site of the next generation of star formation. "Our galaxy grew, and it grew up by growing out," Ness said.'