Astronomers measure the rotation of a supermassive black hole for the first time

Astronomers have for the first time measured the rotation of a supermassive black hole using the wobbling of gaseous material from a disintegrated star. The results, obtained by an international team of scientists, offer a new way to study supermassive black holes and their evolution in the Universe. One of the lead authors of the study published in the prestigious journal Nature was Michal Zajaček from the Masaryk University, Faculty of Science.

23 May 2024 Michal Zajaček

A research team of astronomers from the Massachusetts Institute of Technology (MIT), Masaryk University, NASA and other institutions has a new way to measure how fast a black hole is spinning, using the wobbling gaseous debris from the tidally disrupted star. The scientists have shown that the wobble of the newly formed accretion disk is the key to determining the actual rotation of the central black hole.

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Schematic figure showing the periodic wobble of an accretion disk formed from the remnants of a tidally disrupted star. The left panel shows the precession phase, when the accretion disk is approaching the configuration when it is seen from the edge, resulting in a smaller observed disk area and therefore its lower luminosity. The observer mainly sees the cooler, outer parts of the wobbling disk. The right panel shows the near-frontal phase of precession, when the visible area of the disk is larger and hence its luminosity increases. The inner, hotter parts of the disk are then fully exposed. Credit: Michal Zajaček/MUNI.

"When a star approaches the supermassive black hole from any direction, the newly formed disk is usually misaligned with respect to the black hole's rotation. In a strongly curved spacetime, the disk is pulled along by the black hole's rotation, causing it to precess periodically. It has long been expected that this should lead to the periodic variability of the disk emission. For the first time, we were able to detect this effect and use it to determine the rotation of the black hole. The recorded AT2020ocn event served as a true black-hole laboratory," explains Michal Zajaček from the Department of Theoretical Physics and Astrophysics at the Faculty of Science of Masaryk University, who is one of the lead authors of the study and who applied several models of accretion disks to the measured X-ray bursts to derive the black hole's rotation rate.

The research was partially funded by NASA, the European Space Agency, and the Grant Agency of the Czech Republic.

Further information:

For details of the published study, including contacts and other background information, see the original article HERE.

Visualization of the phenomenon in the attached video HERE. Source: MIT

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