Illustration of a tidal disruption event . A novel technique by MIT and NASA scientists employs accretion disk wobbles from TDEs to measure black hole spins, offering insights into their evolution by tracking X-ray flashes. Credit: Carl Knox – OzGrav, ARC Centre of Excellence for Gravitational Wave Discovery, Swinburne University of Technologyspins using the wobbling of accretion disks resulting from tidal disruption events.
“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,” says Pasham, who is a member of MIT’s Kavli Institute for Astrophysics and Space Research., the University of Leeds, the University of Syracuse, Tel Aviv University, the Polish Academy of Sciences, and elsewhere.
But in recent years, physicists have proposed that, in instances such as during a tidal disruption event, or TDE, scientists might have a chance to track the light from stellar debris as it is dragged around. Then, they might hope to measure the black hole’s spin. From the optical data, the flash appeared to be the first moments following a TDE. Being both bright and relatively close by, Pasham suspected the TDE might be the ideal candidate to look for signs of disk wobbling, and possibly measure the spin of the black hole at the host galaxy’s center. But for that, he would need much more data.
Pasham and his colleagues looked through NICER’s observations of AT2020ocn over 200 days following the initial detection of the tidal disruption event. They discovered that the event emitted X-rays that appeared to peak every 15 days, for several cycles, before eventually petering out. They interpreted the peaks as times when the TDE’s accretion disk wobbled face-on, emitting X-rays directly toward NICER’s telescope, before wobbling away as it continued to emit X-rays .