A team of Chinese researchers from Anhui Normal University, National Astronomical Observatories of the Chinese Academy of Sciences, Sun Yat-sen University, University of Science and Technology of China, and Guangzhou University detected, for the first time, an X-ray quasi-periodicity signal originating from a stellar tidal disruption event (TDE) by an intermediate-mass black hole (IMBH). Published in Nature Astronomy on February 28, 2025 (Beijing Time), this breakthrough discovery provides a new evidence for the existence of IMBHs, which are the missing link between stellar-mass black holes (5-50 solar mass) formed from the core collapse of massive stars, and supermassive black holes (>10⁶ solar mass) residing in the centers of most galaxies.

Thought to be seeds that will eventually grow to become supermassive black holes, IMBHs are especially elusive, and thus very few robust candidates have ever been found. When a star passes too close to a black hole, it is torn apart by the black hole’s immense tidal forces, resulting in its accretion and the release of intense, transient electromagnetic radiation. These TDEs offer critical observational opportunities to detect and study different types of black holes, especially those inactive or dormant.

With detailed timing analysis of the X-ray data obtained from the European Space Agency’s XMM-Newton satellite, the research team detected a unique X-ray signal that oscillated over a period of 85 seconds, from a previously suggested IMBH TDE candidate. This type of quasi-periodic oscillation is a distinctive signature of accretion onto compact objects such as black holes. Similar signals with shorter periods have previously been identified in several stellar-mass black hole systems, and the period has been found to correlate with black hole mass. Combined with the results from X-ray spectral analysis, the detection of the X-ray quasi-periodicity signal allows for joint constraints on the black hole mass, which is in the range of 9,900 to 16,000 solar masses, placing it within the predicted range of the IMBH population, and on the dimensionless spin, which falls between 0.26 and 0.36.

This study opens a new window for observational confirmation of IMBHs through the X-ray timing analysis of TDEs, filling the critical gap in the black hole mass spectrum. The discovery not only provides new insights into the physical properties of IMBHs, but also establishes a foundational methodology for future detailed investigations of IMBH TDEs, e.g., the candidates discovered by the Einstein Probe mission.

Quasi-periodic oscillation signal and power density spectrum of X-ray emission from the IMBH TDE 3XMM J215022.4−055108. The optical image on the left is from Lin et al. (2020, ApJL, 892, 25).

The full paper is available at: https://www.nature.com/articles/s41550-025-02502-0