for National Geographic News
The sun and Earth will probably be spun out into a lonely region of space when the Milky Way and Andromeda galaxies finish colliding about five billion years from now, researchers say in a new study.
There's also a small chance that our solar system will be swept from its home in the Milky Way and scooped up by Andromeda during an earlier close encounter, in just three-and-a-half-billion years.
These predictions stem from a new theoretical model that provides the best look yet at how and when the cosmic pile-up will occur.
The model is the first to trace the probable fate of our own solar system as the galaxies merge. (Related: "Solar System Is 'Bullet Shaped' [May 10, 2007].)
Like a pair of circling skaters, the Milky Way and Andromeda will brush past each other and separate again twice before fusing into a single galactic entity—an elliptical galaxy dubbed "Milkomeda" by researchers—on their third and final encounter.
The first close contact between the Milky Way and Andromeda will also come sooner than had previously been thought—just two billion years from now, say model creators T.J. Cox and Avi Loeb. Both scientists work at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
At that time, Loeb noted, the sun will be an aging but still very active star.
"The fact that this merger will take place before the sun dies is very interesting," he said. "There will still be a solar furnace ... potentially allowing life [on Earth] to still exist."
The work is presented in a paper submitted for publication to the Monthly Notices of the Royal Astronomical Society and is available online from the Harvard-Smithsonian Center for Astrophysics.
What's the World Coming To?
Scientists have known for some time the Milky Way and Andromeda are sailing toward one another at about 75 miles (120 kilometers) per second. Less certain is the rate at which Andromeda is slipping sideways, perpendicular to its line of approach.
Based on recent findings, Cox and Loeb's model assumes that Andromeda's sideways velocity is relatively small, making a collision with the Milky Way inevitable.
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