Outcast Star Zooms Out of Milky Way Galaxy Tue Feb 8, 2005 04:51 PM ET
By Deborah Zabarenko WASHINGTON (Reuters) - An outcast star is zooming out of the Milky Way, the first ever seen escaping the galaxy, astronomers reported on Tuesday.
The star is heading for the emptiness of intergalactic space after being ejected from the heart of the Milky Way following a close encounter with a black hole, said Warren Brown, an astronomer at the Harvard-Smithsonian Center for Astrophysics.
The outcast is going so fast -- over 1.5 million mph -- that astronomers believe it was lobbed out of the galaxy by the tremendous force of a black hole thought to sit at the Milky Way's center. That speed is about twice the velocity needed to escape the galaxy's grip, Brown said by telephone.
"We have never before seen a star moving fast enough to completely escape the confines of our galaxy," he said. "We're tempted to call it the outcast star because it was forcefully tossed from its home."
The star used to be part of a binary pair, waltzing with its companion star close to the rim of the black hole. In this case, "close" is a relative term; the actual distance was probably about 50 times the 93 million-mile distance between Earth and the sun.
As the two stars twirled around each other, they were pulled faster and faster toward the edge of the black hole, one of those monster drains in space whose gravity is so strong that nothing, not even light, can escape once it is consumed.
While the companion star was captured by the black hole, the outcast continued on its whirling path around its edge.
Objects go faster the closer they get to black holes and this star was probably moving at extraordinary speed, perhaps as high as 20 million mph. That very speed, coupled with the speed of its twirling, sent the outcast zooming toward the edge of the Milky Way and beyond.
At this point, the outcast is about 180,000 light-years from Earth, in an outer region of the galaxy known as the halo. A light-year is about 6 trillion miles, the distance light travels in a year
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