Supermassif black hole

Black holes supermassifs in the center of the galaxies

There exists today of many observations which show that about all the grosses Galaxie S have a supermassif black hole in their center, as it is the case in our own galaxy, the Milky Way. The clearest observations of the presence of such a Black hole in our galaxy are those of the orbital movement of the star S nearest to the galactic Center, in the area called Sagitarius A*. The follow-up of the trajectories made it possible to measure the mass of the central black hole directly: 2,6 ± 0,2 million solar masses. In 2002, Astronome S followed the star S2 in Sagitarius A*, and could show that it approached at a distance as small as 17 hours light the central black hole.

Properties

By comparison with a stellar Black hole, the average Densité of a supermassif black hole can in fact very weak being - sometimes weaker than that of the Eau. That is explained by the fact why the Rayon of Schwarzschild of the black hole grows correlatively with the mass, which induces that the density decrease according to the square of the mass: the taller the black hole is, plus his average density falls, even if its mass grows unbounded. Another notable fact, the forces of tides are negligible in the vicinity of the Horizon of the events of a supermassif black hole, because the gravitational Singularité central in is very distant. With the result that an explorer approaching a supermassif black hole would not feel anything in particular during his crossing of the horizon.

Formation

The training of the black holes supermassifs is still strongly discussed since it is certainly done on large scales of time, to compare with the training of a stellar black hole at the time of a Supernova, produced by a massive star, like a star Wolf-Rayet.

The simplest assumption of the training of the black holes supermassifs is obviously to begin with a stellar Black hole which then will accrétera of the matter on billion Année S. This assumption has many defects however, among which the need for a very great density of stars for continuously nourishing the black hole. But especially, of the observations showed the existence of black holes supermassifs to very large Redshift S, i.e. at the beginning of the evolution of the universe. These black holes thus did not have time to be formed by simple star accretion. It is possible that the training of such black holes is in fact very fast at the beginning of the universe.

The satellite Chandra also made it possible to observe in the center of the Galaxie NGC 6240 two black holes supermassifs orbits one around the other of it.

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