For the first time, the American space telescope Chandra has unearthed 70 “ultramassive” black holes: galactic monsters can gather up to ten billion times the mass of the Sun.
Astrophysicists have never before detected such monsters: the largest black holes in the Universe have been identified in 72 clusters of galaxies located up to 3.5 billion light-years from Earth. These black holes can reach masses equivalent to ten billion times that of the Sun. A record, which justifies the epithet “ultramassive” compared to “supermassive”, which is used to refer to black holes a few million times the solar mass, like that of the Milky Way. Our galaxy is home to a black hole of only 4 million solar masses, which is a rickety compared to ultramassive black holes.
To find these cosmic supermonters, Julie Hlavacek-Larrondo, Professor in the Department of Physics at the University of Montreal (Canada) and Mar Mezcua from the Institute of Space Science in Barcelona (Spain) used the Chandra Space Telescope as well as the VLAN (Very Large Array) radio network in New Mexico (United States). Their work was published in the Monthly Notices of the Royal Astronomical Society on February 11, 2018. The two astrophysicists looked in very specific places knowing that clusters of galaxies harbor very massive black holes. And they were not disappointed!
Black holes grow faster than their galaxy
To determine the mass of the black holes, two methods can be used: the first involves measuring how fast the stars surrounding the black hole move, allowing scientists to estimate the gravitational effect of it and deduce its mass. This method indicates that the mass of the black hole goes with that of the galaxy: the more a galaxy is massive, the bigger is also its black hole.
The second measures the amount of X and radio radiation emitted by the material waiting to be swallowed by the black hole. The bigger it is, the higher its emissions are in intensity. “We found that the X and radio emissions of these black holes showed a mass ten times greater than that assumed by the mass of their galaxy. The black holes seem to have had the chance to grow faster than their galaxy,” says Julie Hlavacek-Larrondo. A troubling case as it is generally accepted that black holes in the center of galaxies grow at the same rate as their host.
To explain this, the two researchers have a hypothesis that has yet to be tested. “In these regions there are gigantic quantities of gas that the black hole can swallow and grow,” says Julie Hlavacek-Larrondo. “We believe that this process is at work. “