"Ultramassive" black holes with masses of tens of billions of suns can occur in the Universe much more often than it seems, although astronomers cannot understand how they managed to grow to such gigantic sizes.
In the active centers of large galaxies, from our Milky Way to distant and inaccessible clusters, there are supermassive black holes. By absorbing clouds of gas and stars, merging with other black holes, they can gain mass in many tens of billions of solar masses, influencing the growth and evolution of their galaxies. However, such "ultramassive" giants take a long time to grow, and they are rare in the modern Universe. The current record holder - the quasar S5 0014 + 81 in the constellation Cepheus - can reach 40 billion solar masses. But most of the known supermassive black holes are measured in orders of the hundreds of thousands to hundreds of millions of suns.
However, new work by an international group of astrophysicists indicates that we may grossly underestimate the prevalence of "ultramassive" black holes. University of Montreal professor Julie Hlavacek-Larrondo and her colleagues have studied 72 galaxies located in the brightest and largest clusters at a distance of 3.5 billion light years. Scientists have compared their masses to the masses of supermassive black holes at their centers. The results of the work are presented in an article published by the Monthly Notices of the Royal Astronomical Society and presented on the arXiv.org preprint service.
Observations by the Chandra space telescope made it possible to register X-rays from accretion disks of matter and, based on this, estimate the masses of black holes. The luminosities of the galaxies themselves in the radio range made it possible to estimate their own masses and to compare the obtained figures. As you might expect, the larger the galaxy, the larger the black hole in its center, but overall, the growth in the size of black holes is faster than galaxies.
The dependence of the sizes of galaxies and their supermassive black holes turned out to be nonlinear, and the black holes in the largest of them are much heavier than one might think. So, about 40 percent of the galaxies considered by scientists contained "ultramassive" black holes with masses of 10 billion suns or more. The surprising rate of their growth remains to be explained. Perhaps they began to form under ideal conditions and grew faster than might be expected. Or perhaps we are missing something important in understanding the growth mechanisms of supermassive black holes.
Sergey Vasiliev
