Collisions of black holes should not normally be accompanied by a flash of electromagnetic waves but by gravitational waves and a single resulting black hole. However, such a flash was observed with a wave source detected by Ligo and Virgo. A scenario explains this phenomenon which should recur periodically if it is exact.
Gravitational waves: their detection explained in one minute That’s it, gravitational waves have been detected. These fluctuations in space-time come from the fusion of two black holes about 30 times the mass of our Sun. Discover in this video how Ligo scientists were able to make these first measurements.
Following the detection of GW150914, the first source having produced a gravitational wave directly highlighted on Earth thanks to the Laser Interferometer Gravitational-wave Observatory (Ligo), the astrophysicists were surprised. Indeed, the analysis of the signal showed that the wave resulted from a fusion of two black holes forming a binary system with, as regards the most probable estimates of the masses of the two black holes, respectively 29 and 36 masses solar. However, the rare stellar black holes detected do not exceed 15 solar masses and we therefore do not understand very well how these compact stars could have formed.
To try to solve this conundrum, the researchers proposed various scenarios. One of them involves a process called hierarchical fusion in the accretion disc of a supermassive black hole in the heart of galaxies, more precisely when we are in the presence of an active nucleus of galaxies. In this type of nuclei supplied with gas very often by filaments of cold matter, as cosmologist and astrophysicist Romain Teyssier explained to Futura, stars and black holes will tend to concentrate.
In fact, in the accretion disc surrounding the giant central black hole, the friction forces in a way caused by the gas present will tend to sediment – so to speak – the black holes of classic stellar masses. However, calculations carried out during simulations show that there then exists a ring located approximately 300 times the radius of the horizon of the events of the central black hole, which becomes the place of an accumulation of the stellar black holes where they are found. trapped. They will tend to form binary black holes by capture which will, in turn, tend to merge to give more massive black holes which will be captured, etc. In the end, we are faced with the equivalent of the accretion processes that form the planets in the protoplanetary discs.
We cannot help but think of this scenario following the publication of an article in Physical Review Letters by an international team of astrophysicists and in free access on arXiv. It is based on the detection of gravitational waves emitted by the source S190521g, on May 21, 2019, by Ligo and Virgo. The analysis of the signal again shows that it is a fusion of black holes, but the final compact star would break a record since it is estimated that it would be a black hole of about 150 solar masses. In addition to the fact that it is necessarily the product of two particularly massive black holes, it has been possible to locate S190521g well enough to suggest that it occurred near the supermassive black hole manifesting itself under the shape of a quasar: J1249 + 3449. We are therefore visibly in the situation where the hierarchical growth scenario, previously mentioned, could apply.
This location is all the more interesting as it would be accompanied by a counterpart in the field of electromagnetic waves. Indeed, approximately 35 days after the detection of S190521g, observations carried out with the help of the Zwicky Transient Facility (ZTF) telescope managed by the famous Caltech, and located at the legendary Palomar Observatory near San Diego, revealed an abrupt variation in shine of the quasar which lasted for about 40 days.
Astrophysicists have verified that this eruption was atypical by its power compared to those that have been detected for about 15 years by monitoring and studying J1249 + 3449. In fact, this flash of the