New Hubble observations suggest a dramatic origin story for one of the fastest stars ever detected, involving a tragic encounter with a black hole, a lost companion and swift exile from the galaxy.

The star, HE 0437-5439, is one of just 16 so-called hypervelocity stars, all of which were thought to come from the center of the Milky Way. The Hubble observations allowed astronomers to definitively trace the star's origin to the heart of the galaxy for the first time.

Based on observations taken three and a half years apart, astronomers calculated that the star is zooming away from the Milky Way's center at a speed of 16 million miles per hour – three times faster than the sun.

"The star is traveling at an absurd velocity, twice as much as it needs to escape the galaxy's gravitational field," said hypervelocity star hunter Warren Brown of the Harvard-Smithsonian Center for Astrophysics, who found the first unbound star in 2005, in a press release. "There is no star that travels that quickly under normal circumstances – something exotic has to happen."

Earlier observations linked the star to a neighboring galaxy, the Large Magellanic Cloud. But Brown and his colleagues claim that the new Hubble observations settle the question of the star's origin squarely in favor of the Milky Way.

One reason the star's home was under debate is its bizarrely youthful appearance. Based on its speed, the star would have to be 100 million years old to have traveled from the Milky Way's center to its current location, 200,000 light-years away. But its mass – nine times that of our sun – and blue color mean it should have burned out after only 20 million years.

The new origin story reconciles the star's age and speed, and has all the makings of a melodrama. A hundred million years ago, astronomers suggest, the runaway star was a member of a triple-star system that veered disastrously close to the galaxy's central supermassive black hole. One member of the trio was captured, and its momentum was transferred to the remaining binary pair, which was hurled from the Milky Way at breakneck speed.

As time passed, the larger star evolved into a puffy red giant and devoured its partner. The two merged into the single, massive, blue star called a blue straggler that Hubble observed.

This bizarre scenario conveniently explains why the star looks so young. By merging into a blue straggler, the two original stars managed to look like a star one-fifth its true age.

The findings were published online July 20 in a paper in The Astrophysical Journal Letters.

The team is hunting for the homes of four other unbound stars, all zooming around the fringes of the Milky Way.

"Studying these stars could provide more clues about the nature of some of the universe's unseen mass, and it could help astronomers better understand how galaxies form," said study coauthor Oleg Gnedin of the University of Michigan in a press release.

Images: NASA/ESA/G. Bacon (STScI)

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