What a shock! On Tuesday, May 21 at 5:02 a.m., the astronomers of the LIGO / Virgo collaboration recorded an extraterrestrial signal betraying the hatching, about 7 billion years ago, of an unseen object, particularly imposing: a black hole 142 times more massive than our Sun. It’s 1.7 times heavier than the largest black hole identified so far by this new detection technique, which earned its pioneers the Nobel Prize in Physics in 2017.
Unlike other astronomical instruments, which “see” various wavelengths (visible light, X-rays, infrared, etc.), LIGO and Virgo record jolts in space-time, called gravitational waves, equivalent to wavelets left at the surface of a pond by the throw of a stone. These waves, predicted by Einstein’s theory of relativity, and left unstoppable, are caused by the movement of very massive objects. This cosmic tidal wave leaves only fine lines when it arrives on Earth, but they are enough for physicists to trace their particularly cataclysmic origin.
The imposing black hole, dubbed GW190521, is the result of the fusion of two other giant black holes, respectively 85 and 66 times heavier than our Sun, which approach each other in a fatal spiral. Four turns of this cosmic dance in a tenth of a second were recorded by instruments installed in the United States and Italy and detailed in two articles published on September 2 in Physical Review Letters and Astrophysical Journal Letters.
“Like a missing link”
This record mass is not the main interest of this discovery. “This black hole is like a missing link for us. This is the first time that we have spotted such an object of more than 140 times the solar mass ”, specifies Michela Mapelli, from the University of Padua, Italy, and member of the LIGO / Virgo collaboration. More precisely, the newcomer falls between the two types of black holes known until then. There are the “stellar” black holes, residues of the explosion of massive stars and the concentration of the remaining matter. And those called “super-massive”, more than 100,000 times the mass of our Sun and which nest in the heart of galaxies, having grown by engulfing enormous quantities of galactic matter.
In the so-called intermediate zone, there was until now only one desert, only populated by a few “candidates” (all at least a hundred times heavier than GW190521) identified by radiation caused by the heating of matter at their neighborhood. “This is the first solid detection of a so-called intermediate black hole”, underlines Félix Mirabel, emeritus researcher at CEA and professor at the Institute of Astronomy and Space Physics in Buenos Aires (Argentina). “The origin of supermassive black holes is still debated. One hypothesis is that it results from the fusion of intermediate population objects ”, recalls Olivier Godet, teacher-researcher at the Institute for Research in Astrophysics and Planetology of Toulouse and co-discoverer, in 2009, of one of these candidates with an intermediate mass about 10,000 times heavier than the Sun.
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