Supermassive Black Holes May Be All Over the Damn Place
According to astronomers, even the quietest regions of space may be populated by sky-chewing black holes.
Galaxy NGC 1637. Image: ESO/Digitized Sky Survey 2
A supermassive black hole has been discovered in what was assumed to be a cosmic desert, raising the possibility that these space-shredding behemoths are much more common across the universe than once assumed. This is according to a team of University of Berkeley astronomers who describe this week in Nature the discovery of a black hole of some 17 billion solar masses, e.g. 17 billion times the mass of our Sun, within the old and relatively docile galaxy NGC 1600.
Until now, supermassive black holes have been observed at the cores of very large galaxies in regions of space populated by other very large galaxies. The current supermassive black hole record holder at 21 billion solar masses, for example, lives within the Coma Cluster, an intense zone featuring some of the most dense known galaxies.
While NGC 1600 isn't exactly empty space, it's not the Coma Cluster either. A 2007 paper noted its similarities to "fossil clusters" of galaxies. In a Berkeley statement, Chung-Pei Ma, the leader of the discovery team, likened the supermassive black hole discovery to finding a skyscraper out in some countryside. We expect them in major cosmic "cities," like the Coma Cluster, but not planted in the middle of some Nebraskan cornfield, e.g. NGC 1600.
"Rich groups of galaxies like the Coma Cluster are very, very rare, but there are quite a few galaxies the size of NGC 1600 that reside in average-size galaxy groups," Ma said. "So the question now is, 'Is this the tip of an iceberg?' Maybe there are a lot more monster black holes out there that don't live in a skyscraper in Manhattan, but in a tall building somewhere in the Midwestern plains."
The discovery comes courtesy of observations gleaned from the MASSIVE Survey (which Ma is also the head of), whose mission is to study the structure, dynamics, and histories of the 100 most massive early-type galaxies within 108 megaparsecs (300 million light-years or so) of Earth.
It's likely that NGC's black hole is the remnant of a quasar born in the early universe. "Black holes with masses of about [10 billion solar masses] are observed as quasars in the young Universe," the current paper explains. "Finding the dormant-black-hole descendants of these luminous quasars and understanding their ancestral lineages have been strong motivations for the search for very massive black holes nearby."
A curious feature of NGC 1600 is that its central stars follow circular, rather than elliptical orbits, around the galaxy's black hole center. According to Ma and her team, this may indicate that the supermassive black hole is really a pair of very tightly orbiting black holes, e.g. a binary system. If this were the case, it may be possible to register the effects as gravitational waves. In the meantime, the MASSIVE Survey will continue, hopefully offering more evidence that supermassive black holes are indeed everywhere.