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Supermassive black hole makes a break for it, escapes its galaxy -
June 6, 2012
2 other people
"At the center of nearly every large galaxy lies a supermassive black hole (SMBH), millions or billions of times more massive than the Sun. Not every SMBH needs to be associated with a galaxy, however—it may be possible for a SMBH to escape if it receives a strong kick during a galaxy collision. Astronomers using the Chandra X-ray observatory report they have witnessed one of these unusual events, in which the bright nucleus of a galaxy is not actually located at the galactic center. As they describe in a forthcoming Astrophysical Journal paper, F. Civano et al. identified a candidate SMBH using the Chandra COSMOS survey. Follow-up observations with the Hubble Space Telescope revealed a compact object moving away from another bright object within the galaxy. Both of these bright objects look like galactic cores, but only one of them appears to contain a black hole, and it's the one that is moving. The hunt for rogue SMBHs is related to an important question in galactic astronomy: how do SMBHs grow so huge? Since astronomers know small galaxies merge to make larger galaxies, it's likely the black holes at their centers will also merge. Several galaxies appear to contain two SMBHs, lending support to this idea. At this point, the black holes may fall into mutual orbit, but it's possible for one of them to be flung out through an effect known as a gravitational slingshot. If the SMBHs orbit each other, they emit gravitational radiation, which, according to general relativity, causes their orbits to degrade until they merge. (Gravitational radiation can be observed indirectly through the behavior of pairs of neutron stars, but has yet to be detected directly. Gravitational waves travel at the speed of light and, due to the weakness of gravity, pass through nearly every obstacle.) However, calculations show that a SMBH collision should produce a burst of gravitational waves, which could impart momentum to the single black hole that results, sending it lurching out of...
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