Influence of a black hole's spin: First evidence of precession in ultraluminous accretion disks

Gas swirls around a black hole (BH) owing to the intense gravity of the BH, forming an accretion disk. These accretion disks, being among the most efficient energy conversion mechanisms in the universe, emit light and plasma jets. When a BH spins on its axis, the accretion disk wobbles like a spinning top. This precessional motion has been studied in less luminous accretion disks, but it is unclear if the same phenomenon occurs in ultraluminous accretion disks that emit strong radiation.

Researchers at University of Tsukuba conducted a large-scale radiation electromagnetic hydrodynamics simulation based on general relativity and demonstrated for the first time that the precessional motion of a tilted ultraluminous accretion disk is caused by the spin of the BH. Furthermore, this precessional motion periodically changes the direction of the jets and radiation emitted from the BH, which indicates that the periodic fluctuations in luminosity of ultraluminous accretion disks may be caused by the spin of the BH. The cause of such periodic fluctuations has previously been unknown.

In the future, the researchers intend to validate whether BHs are spinning by comparative analyses between extended-term simulations and observational data. This pioneering achievement is poised to deepen our understanding of how the spin of a BH influences cosmic phenomena, and make a substantial contribution to the authentication of the spacetime framework of BHs and general relativity.

This work was supported by JSPS KAKENHI Grant Numbers 23K03445(Y.A.), 21H01132(R.T.), 21H04488, 18K03710(K.O.). This work was also supported by MEXT as "Program for Promoting Researches on the Supercomputer Fugaku" (Structure and Evolution of the Universe Unraveled by Fusion of Simulation and AI; Grant Number JPMXP1020230406) and used computational resources of supercomputer Fugaku (RIKEN Center for Computational Science, Project ID: hp230204, hp230116), ATERUI II (National Astronomical Observatory of Japan), Oakforest-PACS (the University of Tokyo, University of Tsukuba), and Wisteria/BDEC-01 Odyssey (the University of Tokyo).