Milky Way will be hit head-on

Andromeda galaxy will smash directly into ours

The monstrous Andromeda galaxy and the Milky Way are destined to hit head-on, not in a glancing blow, new observations from the Hubble Space Telescope show.

Four billion years from now, a collision between the Milky Way (left) and Andromeda (right) galaxies will have ripped out streams of stars, warped the galactic shapes and turned Earth’s night sky into a dramatic swirl of starlight. NASA, ESA, Z. Levay and R. van der Marel/STScI, A. Mellinger

By precisely locating the same stars in Andromeda in 2002 and then again in 2010, astronomers at the Space Telescope Science Institute in Baltimore have calculated how the galaxy has moved against the background of deep space — confirming that the galaxy’s sideways motion is but a fraction of the speed at which it’s hurtling toward the Milky Way.

Andromeda is 2.5 million light-years away and closing in on the Milky Way at 250,000 miles per hour. The cosmic collision will transform the heavens into a hallucinogenic swirl 4 billion years from now. Calculations suggest that the sun will be tossed out during this galactic mash-up, to drift erratically in the eventual single, large galaxy that will coalesce from the two.

The work will appear in an upcoming Astrophysical Journal.

Alexandra Witze is a contributing correspondent for Science News. Based in Boulder, Colo., Witze specializes in earth, planetary and astronomical sciences.

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