Milky Way May Escape Fated Collision With Andromeda Galaxy

sciencehabit shares a report from Science.org: For years, astronomers thought it was the Milky Way's destiny to collide with its near neighbor the Andromeda galaxy a few billion years from now. But a new simulation finds a 50% chance the impending crunch will end up a near-miss, at least for the next 10 billion years. It's been known that Andromeda is heading toward our home Galaxy since 1912, heading pretty much straight at the Milky Way at a speed of 110 kilometers per second. Such galaxy mergers, which can be seen in progress elsewhere in the universe, are spectacularly messy affairs. Although most stars survive unscathed, the galaxies' spiral structures are obliterated, sending streams of stars spinning off into space. After billions of years, the merged galaxies typically settle into a single elliptical galaxy: a giant featureless blob of stars. A study from 2008 suggested a Milky Way-Andromeda merger was inevitable within the next 5 billion years, and that in the process the Sun and Earth would get gravitationally grabbed by Andromeda for a time before ending up in the distant outer suburbs of the resulting elliptical, which the researchers dub "Milkomeda." In the new simulation, researchers made use of the most recent and best estimates of the motion and mass of the four largest galaxies in the Local Group. They then plugged those into simulations developed by the Institute for Computational Cosmology at Durham University. First, they ran the simulation including just the Milky Way and Andromeda and found that they merged in slightly less than half of the cases -- lower odds than other recent estimates. When they included the effect of the Triangulum galaxy, the Local Group's third largest, the merger probability increased to about two-thirds. But with the inclusion of the Large Magellanic Cloud, a satellite galaxy of the Milky Way that is the fourth largest in the Local Group, those chances dropped back down to a coin flip. And if the cosmic smashup does happen, it won't be for about 8 billion years. "As it stands, proclamations of the impending demise of our Galaxy appear greatly exaggerated," the researchers write. Meanwhile, if the accelerating expansion of the universe continues unabated, all other galaxies will disappear beyond our cosmic event horizon, leaving Milkomeda as the sole occupant of the visible universe. The study is available as a preprint on arXiv.

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