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Runaway black hole headed our way

By Richard Stenger

The companion star to black hole GRO J1655-40
The companion star to black hole GRO J1655-40

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(CNN) -- In a first, astronomers spotted a black hole streaking through the Milky Way and approaching our nook of the galaxy.

The superdense object is traveling through the galactic plane at about 250,000 mph (400,000 km/h), four times faster than the average speed of stars in its vicinity.

But terrestrial residents can relax. The black hole, currently about 6,000 light-years away, will most likely never shake up our cosmic neighborhood.

"It's coming closer but will miss us by 1,000 light-years," said Ray Villard, a spokesman for the Hubble Space Telescope, which helped detect the black hole, called GRO J1655-40.

"I don't know if it will get closer in the future, but interstellar distances are so vast it will probably never get close enough to affect our solar system," Villard said.

Still, by astronomical measures, the distance is comparatively close, considering that the Milky Way is about 90,000 light-years across.

A light-year is the distance that light travels in one year, nearly 6 trillion miles (9.5 trillion km).

Felix Mirabel, lead scientist in the black hole study, thinks that GRO J1655-40 formed in the core of the Milky Way, the primary birthplace for stars in our galaxy.

Like a cannon shot, a cataclysmic supernova explosion spawned the black hole and sent it hurtling in our general direction, according to Mirabel and colleagues, who published their report in the November 19 issue of Astronomy and Astrophysics.

"This is the first black hole found to be moving fast through the plane of our galaxy," said Mirabel, an astrophysicist at the French Atomic Energy Commission and the Institute for Astronomy and Space Physics of Argentina.

Such "cannonball" black holes were predicted in theory, but "GRO J1655-40 is the first one that has been found in the real universe," Mirabel said.

Scientists were able to follow the runaway black hole by tracking its companion star, an elderly red giant from which GRO J1655-40 constantly siphons matter.

Black holes are regions of space so warped and dense that even light cannot escape their grasp. Those with the mass equivalent of 3.5 to 15 stars, like GRO J1655-40, are thought to be collapsed stars.

Supermassive siblings often lurk in galactic centers, including one in the Milky Way. They boast masses millions or billions of times greater than the sun.

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