Scientists have identified the corpse of a galaxy that fell into the Milky Way about 10 billion years ago in what was likely the last major overhaul to our home galaxy during its development.

That’s the conclusion of new research based on 2 billion measurements of how stars within the Milky Way are moving. Those measurements let scientists identify about 33,000 stars that live in our galaxy but were born elsewhere, carried here during a giant galactic collision.

“The Milky Way is a cannibal. It has eaten many dwarf galaxies in the past, and we’ve just found a major one that it ate in the past,” Kathryn Johnston, an astronomer at Columbia University in New York who wasn’t involved in the new research, told Space.com. “This is like a police investigation — this one in particular, because it’s not a galaxy that we can see today. It’s a dead galaxy, so that makes it kind of fun.”

The research is possible because stars contain a fingerprint of sorts of their origin. “When you look at how stars move, they actually retain in their motions [a] memory of the place where they were born,” Amina Helmi, an astronomer at the University of Groningen in the Netherlands who led the new research, told Space.com.

Helmi and her colleagues drew on data from a European project called Gaia, which is mapping the location of 1 billion stars in the Milky Way with unprecedented precision. The team identified a set of about 33,000 of those stars that are moving in a completely different manner compared to the bulk of the Milky Way.

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