Spin of supermassive black hole measured for first time

22 May 2024

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By looking at the swirling hot material of a black hole ‘feasting’ on a star, researchers were able to predict the spin of the cosmic giant.

A new study claims to have found a new way to measure how fast a black hole spins, which could be used to learn more about how they have evolved over time.

The researchers looked at a supermassive black hole and predicted the spin of the cosmic giant by analysing the aftermath of a ‘stellar feasting’ – an event where a black hole rips a nearby star to pieces.

During these events, half of the star is blown away by the black hole’s tidal forces, while the other half is flung around the black hole, creating a rotating disk of swirling hot material. By looking at the flashes produced by this tidal disruption event – or TDE – the researchers learned how much this disk was being affected by the black hole’s spin.

In turn, this data can be used to determine how fast the black hole is spinning – in this particular case, the researchers believe the supermassive black hole was spinning at less than 25pc the speed of light.

The international group of researchers said this is the first time the observations of a wobbling disk following TDE was used to estimate the spin of a black hole. The study’s lead author, MIT Research scientist Dr Dheeraj ‘DJ’ Pasham, said the new method could be used to gauge the spins of hundreds of black holes in the local universe in the coming years.

“By studying several systems in the coming years with this method, astronomers can estimate the overall distribution of black hole spins and understand the longstanding question of how they evolve over time,” Pasham said.

As new telescopes such as the Rubin Observatory come online in the coming years, Pasham believes there will be more opportunities to pin down black hole spins and understand how they evolved over the history of the universe.

“The spin of a supermassive black hole tells you about the history of that black hole,” Pasham said. “Even if a small fraction of those that Rubin captures have this kind of signal, we now have a way to measure the spins of hundreds of TDEs.

“Then we could make a big statement about how black holes evolve over the age of the universe.”

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Leigh Mc Gowran is a journalist with Silicon Republic