New Type of Black Hole Found in CR7 Galaxy
Scientists have speculated that the early universe was populated by "direct-collapse" black holes that grew into the supermassive black holes that form the centers of quasars. Recently, astronomers are reporting to have found one of these supermassive black hole progenitors in our observable universe.
"It's a cosmic miracle," says Volker Bromm of the University of Texas at Austin (UT) in the press announcement from the Harvard-Smithsonian Center for Astrophysics (CfA). The progenitor black holes would have had to form during a rare window of opportunity when cosmic conditions were exactly right - and if it hadn't happened, the universe would look very different today.
The team behind the discovery includes Bromm and Aaron Smith of UT and Avi Loeb of the CfA, and their evidence is presented in the journal, Monthly Notices of the Royal Astronomical Society. The three astronomers say that they determined that the rare type of black hole can be located in a galaxy identified as CR7 by the Cosmic Evolution Survey (COSMOS).
Bromm and Loeb originally theorized the existence of these early-universe black holes back in 2003. Scientists know that black holes are created through the explosive demise of a massive star. Even the supermassive black holes that form the centers of large galaxies most likely originated as smaller "seed" black holes that grew by pulling in gas and merging with other black holes. Over many eons, this process - known as accretion - would bring about a black hole of behemoth proportions.
However, accretion theory cannot account for the supermassive black holes located within quasars. These high-redshift objects were born in an earlier era of the cosmos, making them young galaxies. That means their supermassive black hole centers emerged during a period when the universe was largely free of gas, which had been dissipated by the processes of early star creation.
With no gas to feed the process of accretion, the black holes within quasars must have originated in another way. Bromm and Loeb's theory proposes that it occurred when primordial clouds of gas got compressed within the gravitational field of a dark-matter halo. The mass would have crunched in smaller and tighter while remaining too hot to fragment into stars that would blow away that gas.
Eventually, the mass would turn into a single supermassive star that would directly collapse into forming the "seed" black hole. Thus, the black holes created in this fashion are known as direct-collapse black holes, and they could only have been born during a particular phase in the youth of the universe.
Today, the astronomers can say that direct-collapse black holes are not merely hypothetical - they exist, and one can be found in the CR7 galaxy. Furthermore, NASA has announced the discovery of two other likely direct-collapse black hole candidates, based on data from the Chandra X-ray Observatory.