Detailed age map shows how Milky Way came together
http://phys.org/news/2016-09-age-milky.html
Using colors to identify the approximate ages of more than 130,000 stars in the Milky Way's halo,
Notre Dame astronomers have produced the clearest picture yet of how the galaxy formed more than 13.5 billion years ago.
Astrophysicist Daniela Carollo, research assistant professor in the Department of Physics at the University of Notre Dame, and Timothy Beers,
Notre Dame Chair of Astrophysics, along with research assistant professor Vinicius Placco and their colleagues published their findings in Nature
Physics, including a chronographic (age) map that supports a hierarchical model of galaxy formation. That model, developed by theoreticians over
the past few decades, suggests that the Milky Way formed by merging and accretion of small mini-halos containing stars and gas, and that the oldest
of the Milky Way's stars are at the center of the galaxy and younger stars and galaxies merged with the Milky Way, drawn in by gravity over billions
of years.
