Astronomers have determined the spin rate of a black hole for the first time.
The novel technique, detailed in a paper in the journal Nature, relies on observing the "wobble" of leftover stellar material as it orbits a black hole.
Tidal disruption events (TDEs) are cataclysmic occurrences where the immense gravitational pull of a black hole rips apart a star. Some of the star's material is blown away, while the rest forms a hot accretion disk of stellar material swirling around the black hole. The team demonstrated that the "wobble" of this disk holds the key to determining the black hole's spin rate.
The black hole was found to be spinning at less than 25% the speed of light.
The black hole studied resides at the center of the quiescent galaxy SDSS J135353.80+535949.7, about a billion light-years from Earth. The authors estimate that the black hole is about 700,000 times the mass of our sun. In 2020, NASA's Neutron star Interior Composition Explorer (NICER) mission aboard the International Space Station (ISS) detected an X-ray flare from this galaxy, designated AT2020ocn. After following the X-ray flare for several months, the astronomers recognized that it was generated by a TDE.
They measured the wobble of the bright, hot accretion disk as it was pulled and pushed by the spinning black hole.
The analysis revealed that the black hole is spinning at less than 25% the speed of light—relatively slowly for a black hole. This new technique to measure the spin rates of black holes could help determine the spins of hundreds of black holes in our cosmic neighborhood.
"By studying a larger sample of systems with this method over the coming years, astronomers may estimate the overall distribution of black hole spins and address long-standing questions about how black holes evolve over time," said Dheeraj "DJ" Pasham, lead author of the study from the Massachusetts Institute of Technology (MIT).
This is the first time the wobble of an accretion disk has been used to determine the spin rate of a black hole. Pasham said that new instruments—such as the Rubin Observatory currently under construction in Chile—will help enable such measurements.
"The spin of a supermassive black hole tells you about its history," the astronomer added. "Even if only a small fraction of the black holes Rubin records have a signal like this, we now have a path to measuring the spins of hundreds of tidal disruption events. We can then make substantial statements about how black holes evolve throughout the universe's history."
Summary:
- Astronomers have successfully measured the spin rate of a black hole using a new technique that analyzes the "wobble" of its orbiting accretion disk.
- The black hole is spinning at less than 25% the speed of light and is estimated to be 700,000 times the mass of our sun.
- This technique could be used to measure the spins of hundreds of black holes in the future, providing valuable insights into their evolution and history.