By Dennis Overbye
The apocalypse has been postponed.
Astronomers have long known that the Andromeda galaxy, a.k.a. Messier 31, a swirling city-state of a trillion stars — plus all the accouterments of gas, dust, dark matter and black holes — is rumbling through the cosmos right toward us at 68 miles per second.
Five years ago astronomers using the Hubble Space Telescope calculated that M31 would hit our Milky Way galaxy head on 3.9 billion years from now.
That collision, they said, would initiate a series of do-si-do encounters that would splash streamers of stars and gas across space, and end with the two galaxies merged into a single, supergiant globe of stars.
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