The galaxies' proximity and devolution is a story as old as time: galaxy mergers.
The mashup will happen slowly. "The process of colliding and merging will not be a quick one either: it might take hundreds of millions of years to unfold. These collisions take so long because of the truly massive distances involved."
But the Milky Way has always been a work in progress. Many galaxies, large and small, have combined to add or subtract to the Milky Way's starry profile, according to research from ESA's Gaia spacecraft.
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