A supermassive black hole in the center of H1821+643, a quasar about 3.4 billion light-years away from Earth, is rotating at about half the speed of light.
This composite image of H1821+643 contains X-rays from Chandra (blue) that have been combined with radio data from NSF’s Karl G. Jansky Very Large Array (red) and an optical image from the PanSTARRS telescope on Hawaii (white and yellow). Image credit: NASA / CXC / University of Cambridge / Sisk-Reynés et al. / NSF / NRAO / VLA / PanSTARRS.
“We estimate the actively growing black hole in H1821+643 contains between about three and 30 billion solar masses, making it one of the most massive known,” said Júlia Sisk-Reynés from the Institute of Astronomy at the University of Cambridge and her colleagues.
“By contrast the supermassive black hole in the center of the Milky Way Galaxy has a mass of about 4 million solar masses.”
In their research, the astronomers analyzed data from NASA’s Chandra X-ray Observatory.
They found that the H1821+643 supermassive black hole is located in the bright dot in the center of the radio and X-ray emission.
Because a spinning black hole drags space around with it and allows matter to orbit closer to it than is possible for a non-spinning one, the X-ray data can show how fast the black hole is spinning.
The spectrum of H1821+643 indicates that the black hole is rotating at a modest rate compared to other, less massive ones that spin close to the speed of light. This is the most accurate spin measurement for such a massive black hole.
“Why is the black hole in H1821+432 spinning only about half as fast as the lower mass cousins? The answer may lie in how these supermassive black holes grow and evolve,” the researchers said.
“This relatively slow spin supports the idea that the most massive black holes like H1821+643 undergo most of their growth by merging with other black holes, or by gas being pulled inwards in random directions when their large disks are disrupted.”
“Supermassive black holes growing in these ways are likely to often undergo large changes of spin, including being slowed down or wrenched in the opposite direction.”
“The prediction is therefore that the most massive black holes should be observed to have a wider range of spin rates than their less massive relatives.”
On the other hand, the scientists expect less massive black holes to accumulate most of their mass from a disk of gas spinning around them.
“Because such disks are expected to be stable, the incoming matter always approaches from a direction that will make the black holes spin faster until they reach the maximum speed possible, which is the speed of light,” they said.
The team’s paper was published in the Monthly Notices of the Royal Astronomical Society.
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Júlia Sisk-Reynés et al. 2022. Evidence for a moderate spin from X-ray reflection of the high-mass supermassive black hole in the cluster-hosted quasar H1821+643. MNRAS 514 (2): 2568-2580; doi: 10.1093/mnras/stac1389
