Stars rotate on their axis and the same should be the case with stellar black holes that form from the gravitational collapse of these stars. The same is believed to be true of supermassive black holes at the centers of galaxies, and the theory of quasar radiation significantly incorporates the fact that these black holes are rotating. In the case of our galaxy, digging into the archives of X-ray observations from NASA’s Chandra satellite, astronomers have concluded that our supermassive black hole was also moving at quite a fraction of the speed of light.

The nearest supermassive black hole is right in the middle of the galaxy and has more than 4 million solar masses. After decades of studying the activities of certain stars located near the source of radio waves, we have discovered that sagittarius a*sagittarius a*, Some of these stars experience such a strong gravitational pull that they move in response at a remarkable fraction of the speed of light.

A laboratory for understanding SGR A*, as our central black hole is also called physiquephysique of supermassive black holesupermassive black hole Back KaiserKaiserthis amazing active galactic nucleusactive galactic nucleus, It also helps us test alternatives to relativistic theory GravityGravity D’EinsteinEinstein And even to test the hypothesis of the existence of the fifth power.

You can study SGR A* in this area x-rayx-rayEspecially with the legendary and venerable satellite ChandraChandra From NASANASA, A team of researchers has come up with a new estimate of rotation speedrotation speed About this black hole as she explains in an article published in *Monthly Notices of the Royal Astronomical Society*,

Mathematician Roy Kerr, who discovered the solution to Einstein’s equations describing rotating black holes, tells the saga of black hole theory, the associated singularity problems, and their discovery. To get a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Select “French”. © Vetenskapsakademien

## Extreme black holes and cosmic censorship

If one believes, not only as is now very likely, especially after the images of*Event Horizon Telescope*that we are truly in the presence of the One kerr black holekerr black hole In rotation, Chandra data tell us that the parameter describing this rotation has a value between 0.84 and 0.96. The maximum would be 1 and this would be roughly the same as saying – if we had this image of this black hole as a sphere SolidSolid – that on the surface of this sphereEquatorEquator Rotates at the speed of light. Technically, this is what we call an extreme Kerr black hole and if we imagined that the parameter is greater than 1, we would no longer have any black holes becauseevent horizonevent horizon will disappear revealing the singularity ofspace timespace timeWhat we EstimateEstimate Generally impossible.

This estimate is called in English *cosmic censorship hypothesis*Which can be translated as the hypothesis of cosmic censorship, was put forward in an initially non-mathematically precise form by the Nobel Prize winner in Physics in 1969. mathematicianmathematician Roger Penrose.

Researchers are divided about its validity.

let us remember this general relativitygeneral relativity, a black hole has a precise mathematical form with a very detailed theory behind it. Basically, a black hole is defined by the existence of a boundary around a region from which, to escape, one must exceed the speed of light: the event horizon. we all know the solution the equationthe equation Einstein described a black hole and in addition to an event horizon, they have space-time singularities where the laws of physics, such as causality, are destroyed.

Penrose hypothesized that, despite this, the laws of physics separated singularities from the rest.universeuniversePreventing them from causing problems, by surrounding them with an event horizon.

Observations on supermassive black holes and cosmic censorship. To get a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Select “French”. © PBS Space Time

However, there are situations with rotating and/or charged black holes that make it possible to imagine the disappearance of the event horizon according to the parameters describing these black holes. when they are about to become DiseaseDisease Thus, these are generally referred to as extreme black holes. The video below gives some details on these black holes and cosmic censorship.

Similar studies with the black hole M87* show that the parameter describing its rotation is between 0.89 and 0.91