The Closest Hypervelocity Star Ever Seen

Artist's conception of a hypervelocity star speeding away from a spiral galaxy into the invisible halo of dark matter surrounding the galaxy's visible portions / Ben Bromley, University of Utah
Janet Fang 08 May 2014, 05:31
 
Long ago, this 32-million-year-old star had a partner on its journey through space. But when the pair got a little too close to a black hole, the dance came undone: The black hole pulled in one of the stars, while its intense gravity fired the other one across interstellar space at an amazing rate, turning it into a hypervelocity star.
 
A team led by Zheng Zheng of the University of Utah spotted the star -- called LAMOST-HVS1 -- traveling more than 1 million miles per hour (about 1.6 million km/hr) and three times as far as stars typically move. Of the 20 hypervelocity stars ever discovered, this one is the second brightest and the nearest to us (though it's more than 42,000 light years from Earth).
 
The newly discovered star gets its name from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), located northeast of Beijing. The telescope can capture the spectra from 4,000 stars at once, and that breakdown of a star's light can tell them about its size, temperature, and, velocity. LAMOST-HVS1 actually travels at 1.4 million mph (2.2 milion kph) relative to our solar system, since we're moving as well.
 
According to Zheng, the hypervelocity star probably originated near the center of our Milky Way galaxy. It's traveling so fast, though, that it's now located above the "disk" of the Milky Way, in what astronomers believe to be a halo of dark matter that surrounds the galaxy. The new discovery isn't simply a stellar speed demon, the star could tell astronomers more about this halo.
 
"We can't see the dark matter halo, but its gravity acts on the star," Zheng says in a press release. "We gain insight from the star's trajectory and velocity, which are affected by gravity from different parts of our galaxy."
 
There's a lot to learn: Zheng estimates that adding the dark matter halo to the visible part of our galaxy expands the Milky Way's diameter by a factor of 10, from 100,000 to 1 million light years across. There's much, much more of the mysterious matter we can't see than what we can, but maybe swift stars can tell us something new about the invisible stuff.
 
The work was published in Astrophysical Journal Letters last month. 
 
 
Image: Ben Bromley, University of Utah
 
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