Newfound ‘Kraken merger’ may have been the biggest collision in Milky Way’s history

The Milky Way contains more than 100 billion stars, but it didn’t come by them all honestly. At least a dozen times over the last 12 billion years, the Milky Way collided with a neighboring galaxy and devoured it, swallowing up that neighbor’s stars and mixing them into an ever-growing stew of pilfered suns.

With each galactic merger, the shape, size and motion of our galaxy changed forever, ultimately becoming the iconic spiral we recognize today. Now, in a recent study published in the October 2020 issue of the journal Monthly Notices of the Royal Astronomical Society, researchers have attempted to unwind that spiral. Using artificial intelligence (AI) to match distinct clusters of stars by their ages, motions and chemical compositions, the team found evidence of five large-scale galactic mergers (each involving 100 million stars or more) dating back more than 10 billion years — including one ancient collision that has never been described before.

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