For the first time, astronomers have measured the rotation speed of a black hole

Astronomers have determined for the first time the rotation speed of a black hole.

The new method, detailed in a paper in the journal Nature, is based on observing the "wobble" of stellar matter left behind after being swallowed by a black hole.

Black hole crushing events (scientific name: TDE) are moments when the black hole's giant gravity impacts stars, tearing them into pieces. As a result, part of the star is blown away, the remaining part forms a hot accretion disk, containing stellar material orbiting the black hole. The team of astronomers demonstrated that the "wobble" of this disk is key to determining the black hole's rotation rate.

The black hole rotates at less than 25% of the speed of light.

The black hole studied is located at the center of the quiet galaxy SDSS J135353.80+535949.7 , about a billion light years from Earth. The authors estimate the mass of this black hole to be about 700,000 times that of our Sun. In 2020, NASA's NICER (Neutron Star Internal Composition Explorer) instrument on the International Space Station (ISS) analyzed an X-ray flare from this galaxy, named AT2020ocn . After monitoring the X-ray flares for several months, astronomers realized that the X-rays were produced shortly after a stellar crushing event by a black hole.

They measured the wobble of the bright, hot accretion disk as it was attracted and pushed by the spinning black hole.

Analysis shows that the black hole rotates at less than 25% of the speed of light - relatively slow for a black hole. This new method of measuring black hole rotation could help determine the spin rates of hundreds of black holes near us.

Dheeraj "DJ" Pasham, lead author of the study - from the Massachusetts Institute of Technology (MIT), said: "By studying several systems in the coming years with this method, astronomers "can estimate the overall distribution of black hole rotation rates and understand the long-standing question of how black holes evolve over time."

This is the first time the wobble of the accretion disk has been used to determine a black hole's rotation rate. Author Pasham says that new instruments - such as the Rubin Observatory currently under construction in Chile - will help in such measurements.

The astronomer now adds: " The rotation rate of a supermassive black hole tells you about the history of that black hole . Even if a small fraction of the black holes that Rubin recorded had signals like With this, we now have a way to measure the rotation rates of hundreds of TDEs. We can then make important statements about how black holes evolve over the lifetime of the universe."

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