Giant black hole spins surprisingly slowly compared to other black holes

(ORDO NEWS) — Astronomers have brilliantly produced an extremely complex measurement of a black hole’s own spin rate, one of two fundamental properties of black holes.

According to these results, based on data collected by NASA‘s Chandra X-ray space observatory, the black hole under study rotates much more slowly than other known black holes.

This black hole is the most massive black hole for which its own spin rate has been determined to date, and these data will help to better understand the growth of the most massive black holes in the universe.

“Each black hole can be defined by just two quantities – rotational speed and mass,” said Julia Sisk-Reynes of the Institute of Astronomy at the University of Cambridge, United Kingdom, who led the new study. “It sounds simple, but actually calculating these quantities for black holes is incredibly complex.”

To obtain these results, the researchers observed X-rays reflected from a disk of matter orbiting a black hole in the H1821+643 quasar.

Quasars contain rapidly growing supermassive black holes (SMBHs) that generate large amounts of energy in a small region of space around the black hole.

Located in a cluster of galaxies about 3.4 billion light-years from Earth, the black hole of object H1821+643 has a mass between 3 and 30 billion solar masses, making it one of the most massive black holes known to science. For comparison, the SMBH at the center of the Milky Way has a mass of about four million solar masses.

Strong gravity in the vicinity of a black hole affects the nature of the X-ray intensity distribution over energies, and the faster the black hole rotates, the more profound distortions it produces.

Therefore, by the depth of distortion of this X-ray radiation, scientists can estimate the speed of the black hole’s own rotation.

“We found that the black hole of the H1821+643 quasar rotates about half as slowly as most black holes with masses in the range of one to ten million solar masses,” said co-author Christopher Reynolds, also of the Institute of Astronomy. “The key question is why is this black hole spinning so slowly?”

According to the authors, the explanation could be that high-mass black holes experience collisions with other black holes during their life cycle, and the disk of material around them is torn apart so that the material falls from different directions at different speeds.

At the same time, in the case of small black holes, a stable disk of material is formed that always moves in the same direction, and therefore its fall into the black hole all the time leads to a gradual increase in its rotation speed until it reaches its maximum value, Sisk-Reins and her colleagues believe.

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