Our galaxy is set to merge with its closet neighbor four billion years from now, give or take:
Recent observations confirm that Andromeda is heading straight toward us at about 60 miles per second, and will traverse the 2.5 million light-year distance currently separating our galaxies in about four billion years. While the collision of two galaxies might conjure up images of mass devastation, the event will be largely imperceptible to our descendants, if any are still around. (They will have had to find another home: By that time, the increasing luminosity of our sun will have rendered Earth uninhabitable.) Galaxies are mostly empty space, so almost no stars or planets will actually collide.
Nonetheless, the Milky Way as we know it will cease to exist. Initially, the two galaxies will slide past each other and draw apart until gravity hits the brakes and pulls them back together. As Andromeda and…
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