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Star US 708 Is Hurtling Out Of Milky Way: Here's Why

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Milky Way's fastest known star in on its way out of our galaxy and a new study suggests that a supernova is responsible for giving it the boot.

The star, dubbed US 708, is traveling at a speed of 26 million miles per hour making it the fastest star that astronomers were able to click. At this speed, the star can escape Milky Way's gravitational pull, which will allow it to eventually make its way into intergalactic space.

While most other hypervelocity stars, or HVSs, that speed out of the galaxy are believed to be flung by the enormous gravity of the black hole at the center of the galaxy, researchers said that US 708 appeared to have a different origin.

It is probably launched by the so called Type Ia supernova, one of the universe's brightest and most powerful bursts of energy. What triggers these particular exploding stars remains a mystery but researchers hope that the fast-moving US 708 could offer some clues.

Scientists said that US 708 was likely orbiting another star when it changed path with the duo stars likely orbiting each other fast with a very small distance between them. This neighboring star exploded into a supernova and was destroyed completely. US 708, on the other hand, was suddenly left lacking a gravitational tether that would keep it in the same place. All the energy and rotational speed as a result started to move in a straight line.

"It's like if you are riding a swing carousel, where you are connected with a chain, and you cut the chain - then you fly away from the carousel," Geier said. "In this case the carousel explodes."

US 708, which is classified as a hot subdwarf, was first found in 2005. Astronomers used the Keck II telescope's Echellette Spectrograph and Imager instrument for measuring the star's distance and velocity along our line of sight.

"In reconstructing its trajectory, the Galactic center becomes very unlikely as an origin, which is hardly consistent with the most favored ejection mechanism for the other HVSs," study researcher Stephan Geier, from the European Southern Observatory, and colleagues wrote in their study, which was published in the journal Science on March 6. "According to our binary evolution model, it was spun-up by tidal interaction in a close binary and is likely to be the ejected donor remnant of a thermonuclear supernova."

Photo: ESA/HUBBLE, NASA, S. Geier

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