The Milky Way as we know it today was shaped by a collision with a dwarf galaxy about 10 billion years ago. But most of the modern galaxy was already in place even at that early date, new research shows.
Ages of stars left behind by the galactic interloper are a bit younger or on par with stars in the Milky Way’s main disk, researchers report May 17 in Nature Astronomy. And that could mean that the Milky Way grew up faster than astronomers expected, says study author Ted Mackereth, an astrophysicist at the University of Toronto.
“The Milky Way had already built up a lot of itself before this big merger happened,” he says.
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