The New History of the Milky Way

Astronomers assumed that the Milky Way had a hectic youth, but <a href="/default/tags/helmer-koppelman" hreflang="en">Helmer Koppelman</a>, an astronomer now at the Institute for Advanced Study in Princeton, New Jersey, used the Gaia data to help pinpoint specific debris from one of the largest mergers.

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The galactic wreckage was everywhere. Perhaps half of all the stars in the inner 60,000 light-years of the halo (which extends hundreds of thousands of light-years in every direction) came from this lone collision, which may have boosted the young Milky Way’s mass by as much as 10%. “This is a game changer for me,” Koppelman said. “I expected many different smaller objects.”