Binary supermassive black holes about to merge have been detected

The galaxies host supermassive black holes and some are in fact binary. Eleven of these objects may have been spotted by their periodic gamma rays. The study of supermassive black hole fusions is potentially rich in information, especially because of the gravitational waves that accompany them.

In the interview he gave to Futura a few years ago, the late Pierre Binétruy had not only told us about  Gravity! From Big Bang to black holes ;  his  Mooc ( Massive open online course ) given with the Nobel Prize in physics George Smoot had also made it possible to understand why astrophysicists and cosmologists went in pursuit of gravitational waves .

page accompanies this Mooc (free online course), explaining what are gravitational waves, how to detect them by interferometry and which detector to use). Pierre Binétruy explained the importance of the eLisa space interferometer, planned for 2030, to study the gravitational universe of Einstein . He did so by answering several of our questions. Let us recall some of our discussions on this subject.

Why do we need to build a gravitational wave detector in space?

 Advanced Ligo and Virgo are not suitable for the detection of gravitational waves produced by collisions of supermassive black holes . They only give access to a part of the observable universe. This is not the case for eLisa which is particularly sensitive to the waves emitted by collisions of black holes containing between 10,000 and 10 million solar masses and this, in almost all of the observable cosmos.

The signal produced by these collisions makes it possible to evaluate the mass and the angular momentum of the black holes concerned. However, as eLisa will be able to detect such very ancient events, going back to the first hundreds of millions of years of the observable universe, when stars and galaxies began to form, this instrument should allow us to better understand the history of black holes supermassive. Indeed, we should be able to make statistics on the masses and the angular moments of the populations of giant black holes during the history of the universe.

Massive black holes, those which are not produced directly by the gravitational collapse of a star, grow in mass at the same time as their galaxy. It is not clear what this means. We know, on the other hand, that galaxies can collide and merge, and so it must be the same for massive black holes present in their center. Of binary supermassive black holes have also been spotted in some galaxies thanks to X-rays .

One possible scenario is that lower mass black holes arise in the hearts of young galaxies, then merge successively when one galaxy engulfs another. These black holes can also grow by accreting matter from these galaxies.

In short, there are many uncertainties about the birth of these giant black holes and the mechanisms of their growth. As they can influence the evolution of their host galaxy , for example when they become quasars , eLisa should also help us understand the history of galaxies and therefore that of the Milky Way .