Astronomers find evidence Milky Way grew \'inside out\'

European astronomers say new evidence suggests the Milky Way may have formed from the inside out, expanding out from the center. New observations using a European Southern Observatory telescope in Chile suggests older stars inside the Solar Circle -- the orbit of our sun around the center of the Milky Way, which takes roughly 250 million years to complete -- are far more likely to have high levels of magnesium, suggesting this area contained more stars that "lived fast and died young" in the past. Tracking the amount of chemical elements in a star other than hydrogen and helium -- the two elements comprising most stars -- allows a determination of how rapidly different parts of the Milky Way were formed, the astronomers said. "The different chemical elements of which stars -- and we -- are made are created at different rates -- some in massive stars, which live fast and die young, and others in sun-like stars, with more sedate multibillion-year lifetimes," Gerry Gilmore, lead investigator on the Gaia-ESO Project, said. The important differences in stellar evolution across the Milky Way disc suggest very efficient and short star formation timescales occurring inside the Solar Circle whereas, outside the sun's orbit, star formation took much longer, the researchers said. "We have been able to shed new light on the timescale of chemical enrichment across the Milky Way disc, showing that outer regions of the disc take a much longer time to form," study leader Maria Bergemann from Cambridge University's Institute of Astronomy said.