Astronomers from MIT, NASA, and other institutions have developed a new method to measure the spin of a black hole by studying the aftermath of a tidal disruption event. When a star passes too close to a black hole, the immense tidal forces exerted by the black hole can rip the star apart, resulting in half of it being blown away while the other half forms an accretion disk of rotating stellar material around the black hole. The MIT-led team has shown that the wobble of this newly created accretion disk can be used to determine the black hole’s spin.
In a study published in Nature, the astronomers reported that they were able to measure the spin of a nearby supermassive black hole by tracking the pattern of X-ray flashes produced following a tidal disruption event. By analyzing how the accretion disk wobbled over time, they were able to calculate the speed at which the black hole was spinning, determining that it was spinning at less than 25 percent the speed of light. This new method could potentially be used to measure the spins of hundreds of black holes in the local universe in the future, shedding light on how these gravitational giants have evolved over time.
The study’s co-authors included researchers from various institutions, highlighting the collaborative effort involved in this research. Black holes have an inherent spin that has been influenced by their interactions with other cosmic objects over time. The way a black hole grows, whether through accretion or mergers with other black holes, can affect its spin. As a black hole spins, it drags the surrounding space-time with it, causing a wobbling effect known as Lense-Thirring precession.
During a tidal disruption event, the disk of shredded material created by the disrupted star may be tilted or misaligned with the black hole’s spin, causing it to wobble. Scientists have proposed that tracking this wobbling disk during a TDE can provide valuable insights into the black hole’s spin. Observations of the X-ray flashes emitted by a TDE can help track the wobbling of the accretion disk and estimate the black hole’s spin. In this study, the team analyzed data from the TDE AT2020ocn using the NICER telescope and determined the black hole’s spin to be less than 25 percent the speed of light.
The research team’s findings mark the first time that scientists have been able to estimate the spin of a black hole by observing the wobbling of its accretion disk following a tidal disruption event. With the development of new telescopes in the future, such as the Rubin Observatory, there will be more opportunities to study black hole spins and gain a better understanding of how these massive objects have evolved over the age of the universe. This research was supported by funding from NASA and the European Space Agency, underscoring the importance of international collaboration in advancing our knowledge of black holes and the cosmos.
