Astronomers find a black hole that spins slower than expected and nobody knows why

Thanks to NASA’s Chandra X-ray Observatory, a team of astronomers has made an unprecedented measurement of the spin of a black hole, one of the two fundamental properties of black holes.

NASA’s Chandra X-ray Observatory shows a supermassive black hole at the center of H1821+643, a quasar about 3.4 billion light-years away from Earth, spinning at about half the speed of light ; it spins slower than most of its smaller cousins.

The reason, unknown Supermassive black holes contain millions or even billions of times more mass than the Sun. Astronomers believe that almost all large galaxies have a supermassive black hole at their hearts. While the existence of supermassive black holes is already well known to science – we were recently able to see the first simulation of the Milky Way’s black hole, Sagittarius A* – scientists are still working to understand how these cosmic behemoths grow and evolve.

They have strong gravitational pulls, and nothing, not even light, can escape their grasp. That affects our ability to look at them and their nearby regions. One crucial piece of information is knowing how fast black holes spin. “Every black hole can be defined by just two numbers: its spin and its mass,” says Julia Sisk-Reynes of the Cambridge Institute for Astronomy (IoA), leader of the paper published in the Monthly Notices of the Royal Astronomical Society. “While that sounds simple enough, calculating those values ​​for most black holes has turned out to be incredibly difficult.”

According to data, this actively growing black hole contains between 3 and 30 billion solar masses, making it one of the most massive known. Sagittarius A*, by contrast, has a mass of about 4 million solar masses.

spin slower The astronomers analyzed data from NASA’s Chandra X-ray Observatory. They found that the supermassive black hole H1821+643 is located in the bright spot at the center of radio and X-ray emission. Because a spinning black hole drags space with it and allows matter to orbit closer to it than usual than is possible for a non-rotating one, X-ray data can show how fast the black hole in question is spinning.

Studies of the spectrum of H1821+643 show that the black hole’s rotation speed is strange, compared to other less massive ones that rotate at close to the speed of light; something that surprised the team. Is it because of his way of increasing in size? This relatively slow spin supports the idea that the most massive black holes, like H1821+643, experience most of their growth by merging with other black holes, or because gas is pulled in in random directions when their large disks break apart. . Supermassive black holes that grow in this way are likely to often experience large spin changes, including slowing down or twisting in the opposite direction, experts say. Thus, “the prediction is that more massive black holes should be observed to have a wider range of spin rates than their less massive relatives.”