Milky Way to face a one-two punch of galaxy collisions

Enlarge / A simulation of galaxies forming in the early Universe. By chance, some of them experience a history that's similar to the Milky Way's. (credit: The EAGLE Project)
If our knowledge of galaxy structures was limited to the Milky Way, we'd get a lot of things wrong. The Milky Way, it turns out, is unusual. It's got a smaller central black hole than other galaxies its size; its halo is also smaller and contains less of the heavier elements. Fortunately, we've now looked at enough other galaxies to know that ours is a bit of an oddball. What has been less clear is why.
Luckily, a recent study provides a likely answer: compared to most galaxies, the Milky Way has had a very quiet 10 billion years or so. But the new study suggests we're only a few billion years from that quiet period coming to an end. A collision with a nearby dwarf galaxy should turn the Milky Way into something more typical looking—just in time to have Andromeda smack into it.
Incoming
The researchers behind the new work, from the UK's Durham University, weren't looking to solve the mysteries of why the Milky Way looks so unusual. Instead, they were intrigued by recent estimates that suggest one of its satellite galaxies might be significantly more massive than thought. A variety of analyses have suggested that the Large Magellanic Cloud has more dark matter than the number of stars it contains would suggest. (Its stellar mass is estimated to be only five percent of the stellar mass of the Milky Way.)
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