Astronomers have found new evidence that the Milky Way is a cannibal, devouring streams of stars from its nearest galactic neighbors. The finding lends further support to the idea that instead of forming wholesale, our galaxy grew bit by bit and is even today snaring matter from other galaxies (SN: 4/22/00, p. 261).
The study also raises questions about how and when globular clusters, dense groupings of the oldest stars in our galaxy, were formed. According to a widely accepted view, those clusters that have the lowest abundance of what astronomers refer to as metals–any element heavier than helium–are slightly older residents of the Milky Way than the others. That's because they were presumably born at the very start of the galaxy, when interstellar space wasn't yet polluted with heavy elements.
However, some metal-poor globular clusters might in fact be younger refugees from smaller galaxies in which star formation got a later start, Suk-Jin Yoon and Young