"The black hole has really strong gravity," explained Zheng Zheng, an assistant professor at the U. and lead author of a study published in Astrophysical Journal Letters by a team of American and Chinese astronomers. "When the pair of stars moves closer to the black hole, the gravity is so strong ... it makes the two stars separate from each other."
One of the stars was drawn into the black hole's orbit or possibly sucked inside and the other catapulted into space at tremendous speed. It's now been traveling for some 32 million years and is in the Milky Way's halo of dark matter.
"Dark matter is totally different from the matter we're familiar with," Zheng said. "We have knowledge of dark matter from its gravitational effect on other objects [but] ... we don't know what it is."
Astronomers can learn more about the substance by monitoring the star's position and watching how its motion is affected.
The star can also tell researchers more about the black hole that originally created it, Zheng said.
"So far, this star is the nearest, so it's very easy to do follow-up study," he said. It's one of about 20 hypervelocity stars that have been found during the past decade.
Even though the new star, dubbed LAMOST-HVS1, is the closest one to Earth, it's still about 249 quadrillion miles from this planet. (A quadrillion is 1 million billion).
Astronomers discovered the star using the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, which is 110 miles northeast of Beijing.
With a 13.1-foot-wide aperture, the telescope captures light-wavelength readings of up to 4,000 stars at once. These "spectra" can show researchers the stars' velocity, temperature, luminosity and size.
The new star is nine times more massive than our sun, but researchers say the chances of the black hole hurling a star toward Earth are low. It creates a hypervelocity star only once every 100,000 years, and the possible trajectories of stars nearby don't appear to pose any danger.