Astronomers Uncover Black Hole Choreography

An international team of astronomers – including Tanja Petrushevska, assistant professor at the Center for Astrophysics and Cosmology, University of Nova Gorica (UNG) – has made an important discovery about how black holes behave. They found clear evidence that a black hole’s surrounding disk of gas and the jet of fast-moving particles it launches can move and wobble together in a coordinated way. This discovery, based on the tidal disruption event (TDE) AT2020afhd, has been accepted for publication in the reputable peer-reviewed journal Science Advances.

Tidal disruption events occur when a star gets too close to a supermassive black hole and is torn apart by its gravity. Some of the star’s material forms a bright, hot disk around the black hole, and sometimes a powerful jet of particles is launched. These rare events allow scientists to study how black holes feed and how their jets form.

The TDE AT2020afhd happened in the galaxy LEDA 145386, about 120 million light-years from Earth. After an unusual brightening in January 2024, scientists began an extensive, year-long observing campaign across many wavelengths. Space-based X-ray telescopes – Swift, NICER, and XMM-Newton – monitored the event, while radio observations were carried out with major facilities including the Very Large Array, Australia Telescope Compact Array, e-MERLIN, and Very Long Baseline Array.

Around 215 days after the event began, the team noticed something remarkable. The X-ray brightness showed a strong repeating pattern every 19.6 days, changing by more than a factor of ten. The radio brightness varied in sync with it.

“This cross-band, high-amplitude quasi-periodic behavior strongly indicates that the accretion disk and jet are precessing as a coordinated system,” said Wang Yanan, first author of the study and researcher at the National Astronomical Observatories of the Chinese Academy of Sciences. “It is as if we can ‘see’ the black hole system tilting rhythmically, with its disk and jet moving together.”

This behavior matches predictions of the Lense–Thirring effect, a phenomenon from Einstein’s theory of general relativity where a spinning black hole drags spacetime around with it. Although scientists have expected this effect for decades, finding direct observational evidence has been very difficult.

With more than a year of detailed observations, the team built a model that explains the wobbling motion and matches the X-ray and radio changes. Their results help determine the system’s geometry, the black hole’s spin, and how fast the jet is moving.

Dr. Tanja Petrushevska commented: “This discovery highlights the importance of international collaboration in time-domain astronomy and showcases the growing contribution of the University of Nova Gorica researchers to cutting-edge black hole science.”

The paper is available at: https://www.science.org/doi/10.1126/sciadv.ady9068