Hubble: Andromeda Is Big, Massive, And Full Of The Stars Our Milky Way Is Missing
“The low-density, outer halo contains stars just as ancient as the Milky Way’s oldest: 13+ billion years of age. Andromeda has stellar streams populating that halo, with a third of those stars just 6-8 billion years old.
This means a major act of galactic cannibalism recently occurred.”
Every few years, a new study comes out claiming that the Milky Way may rival the Andromeda galaxy for the status of largest within our local group. Nonsense! Andromeda is practically double the diameter, contains anywhere from 2.5 to 5 times as many stars, and now there’s evidence that it gobbled up a number of massive galaxies relatively recently. Not only does it have stars just as old as the oldest we’ve ever found in the Milky Way, but we now have evidence that, 6-8 billion years ago, it devoured a large member of our local group entirely, with about a third of Andromeda’s halo stars having formed at around that time. When the Milky Way-Andromeda merger finally comes, there can be no doubt that the remnants of Andromeda will dominate whatever’s left.