This black hole spins more slowly than usual, and scientists have a theory as to why

Black holes are measured by two numbers: their mass and the speed of their rotation. Cambridge University astronomers have managed to make a record-breaking analysis of a supermassive black hole in the quasar ‘H1821 + 643’, and found that it spins slower than normal compared to its smaller cousins.

The discovery is unprecedented and could give clues as to how black holes can become ‘supermassive’ – the kind of objects that escape scientific understanding and challenge much of the research on them.

Black holes tend to spin very fast, but for some reason their supermassive cousins ​​may be slower than expected – and we still do not know why.

In fact, supermassive black holes can be billions of times the mass of the Sun. Scientists estimate that each large galaxy has one at its center. This is the case with the Milky Way and also its immediate neighbor, Andromeda. But even though we have already identified several of them, we still do not understand how they manage to become so large.

For this study, the researchers examined X-rays that escaped from a slice of material around the H1821 + 643 quasar. Quasars contain supermassive black holes that grow at an accelerating rate, and their rotations – usually just as fast – tend to pull the space around them, efficiently gathering material and forming a slice.

H1821 + 643 is 3.4 billion light-years from Earth and is between three and 30 billion times the mass of the Sun. Specifically: it is one of the most massive black holes ever discovered. For comparison: Sagittarius A *, our supermassive black hole is “only” four billion times the mass of the Sun.

According to the researchers, the amplified gravitational forces around the black hole change the intensity of X-rays to varying degrees. The larger this change, the closer they will be to the inner ring of the event horizon – a black hole “point of no return” – allowing us to analyze their rotational speed.

“We found that this black hole rotates more slowly, with about half the speed of other black holes weighing between one million and 10 million times the Sun,” Cambridge astronomer and co-author Christopher Reynolds told the study. . “The question that remains unanswered is: why?

The answer is still unknown, but one theory adds weight to the consensus that supermassive black holes grow by fusing or absorbing smaller holes. In this way, supermassive holes are likely to experience changes in their rotational speed, possibly slowing down or even being driven in the opposite direction.

The premise opens up the possibility that supermassive black holes have a larger range of rotation compared to their smaller cousins.

On the other hand, the scientific consensus is that ordinary black holes accumulate most of their masses through a disk of matter orbiting them. Because these discs are relatively stable, fabric entering them does so in a direction that causes the holes to spin faster and faster until they reach maximum speed, ie. speed of light.

“The moderate rotation of this massive object may be a testament to the violent and chaotic history of the largest black holes in the universe,” said co-author James Matthews, also of Cambridge. “He can offer knowledge about what can happen to our galaxy’s supermassive black hole billions of years from now, when the Milky Way collides with Andromeda. »

An article was published and reviewed by the scientific journal Royal Astronomical Society monthly announcements.

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