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Milky Way’s Fastest Stars Are Runaway Stars From Another Galaxy

First Posted: Jul 06, 2017 08:23 AM EDT

The fastest-moving stars in the Milky Way Galaxy are actually runaways from a smaller galaxy in orbit, astronomers have found out. A research team from the University of Cambridge have demonstrated that such fast-moving stars large blue stars, known as hypervelocity stars, originated in the Large Magellanic Cloud (LMC). To date, about 20 hypervelocity stars have been observed -- mostly in the northern hemisphere.

According to a news release by the University of Cambridge, the researchers used computer simulations and data from the Sloan Digital Sky Survey to conduct their study. Incidentally, the LMC is a dwarf galaxy in orbit around the Milky Way. Hypervelocity stars escaped from their original home after the explosion of one star in a binary system resulted in the others flying off with such speed that they were able to transcend LMC’s gravity and get absorbed in the Milky Way.

Before making this discovery that has been published in the Monthly Notices of the Royal Astronomical Society, the astronomers had thought that hypervelocity stars were expelled from the Milky Way’s center by a supermassive black hole, among other various theories. “Earlier explanations for the origin of hypervelocity stars did not satisfy me,” the paper’s lead author, Douglas Boubert, said. “The hypervelocity stars are mostly found in the Leo and Sextans constellations – we wondered why that is the case.”

Runaway stars that originate in the Milky Way Galaxy do not travel quickly enough to be hypervelocity ones because the latter cannot orbit near enough without the two stars merging. However, a fast-moving galaxy, such as the LMC, can give rise to such fast-moving stars. Incidentally, the LMC has only 10 percent of Milky Way’s mass; therefore, the speedy runaway stars born in this galaxy can leave its gravity. In fact, a researcher likened hypervelocity stars to stars that just jumped out from an express train.

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