Black hole on the loose.

Apparently, a black hole has been booted from its nearby galaxy by a powerful cosmic merger of two galaxies. This black hole is now racing out at speeds of approximately six million miles per hour.

"We have observed the pre-merger stages of black holes," said Stefanie Komossa of the Max Planck Institute for Extraterrestrial Physics, part of the team that made the new discovery. "But we haven't seen the actual merger event."

Komossa and her team have now detected the consequences of such a merger: a 100-million-solar mass black hole in the process of leaving its home galaxy.

"The consequence was that the merged black hole, the final product, the new black hole was expelled from the galaxy," Komossa said.

"One possibility is that for a long time they just orbit each other," like binary stars, Komossa told SPACE.com.

Eventually, the orbiting black holes might interact with a star or surrounding gas which could cause them to lose angular momentum. "That would be a way to push them ever-closer towards each other," Komossa said.

Eventually, the black holes would fuse, and "in the final coalescence, or merger, of these two black holes, a giant burst of gravitational waves is emitted," she said. "Since these waves are generally emitted in one preferred direction, the black hole is then kicked in the other direction."

The "kick" the black hole receives is akin to the recoil of a rifle. It can propel the black hole to speeds of up to several thousand miles per second, according to theoretical simulations. The escaping black hole Komossa and her team observed was racing along at 5,900,000 mph.
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