Black Hole Caught Exiting Host Galaxy
June 5, 2012

Black Hole Caught Exiting Host Galaxy

Lee Rannals for

New observations from NASA's Chandra X-ray Observatory suggest that a black hole is being ejected from its host galaxy at several million miles per hour.

The finding could mean that there are many giant black holes that are roaming around undetected out in the vast spaces between galaxies.

"It's hard to believe that a supermassive black hole weighing millions of times the mass of the sun could be moved at all, let alone kicked out of a galaxy at enormous speed," Francesca Civano of the Harvard-Smithsonian Center for Astrophysics (CfA), said in a press release. "But these new data support the idea that gravitational waves -- ripples in the fabric of space first predicted by Albert Einstein but never detected directly -- can exert an extremely powerful force."

Laura Blecha, co-author of the study that will be in the June 10 edition of The Astrophysical Journal, said because the black holes have consumed all the gas surrounding them after being thrown out of a galaxy, they are invisible to us.

The team has been studying the system known as CID-42, which is located in the middle of a galaxy about 4 billion light years away.

They previously spotted two distinct, compact sources of optical light in the CID-42 by using the Hubble Space Telescope.

More data from the ground-based Magellan and Very Large Telescopes in Chile helped supply a spectrum that suggests the two sources in CID-42 are moving apart at a speed of at least 3 million miles per hour.

Previous Chandra observations detected a bright X-ray source that caused super-heated material around one or more supermassive black holes.

"The previous data told us that there was something special going on, but we couldn't tell if there were two black holes or just one," another co-author Martin Elvis, also of CfA, said in a press release. "We needed new X-ray data to separate the sources."

The team used Chandra's High Resolution Camera to show that X-rays were coming only from one of the sources.  The team believes that when the two galaxies collided, the supermassive black holes in the center of each galaxy also collided.

The two black holes then merged to form a single black hole that recoiled from gravitational waves produced by the collision, which gave the newly merged black hole a sufficiently large kick for it to eventually escape from the galaxy.

The other optical source is thought to be the bright star cluster that had been left behind. This picture is consistent with recent computer simulations of merging black holes.