Milky Way, cannibal, dwarf galaxies
Our galaxy might be a cannibal 1. Long ago the Milky Way was one of many small galaxies. Over time it may have consumed its even smaller neighbors 2, growing into the galaxy we know today 3. In support of this scenario, astronomers have discovered that stars in surviving dwarf galaxies orbiting the Milky Way today (detail) have a highly similar chemical composition to stars in the Milky Way's outskirts, a region known as the halo. This, in turn, suggests that halo stars were once part of dwarf galaxies that the Milky Way absorbed. Even now our galaxy continues to eat its brethren.
A snapshot of the modern Milky Way and surviving dwarf galaxies orbiting in and around the galaxy's halo