A recent study conducted by Northwestern University challenges the long-held hypothesis that black holes consume matter slowly. Contrary to previous beliefs, the study reveals that black holes are voracious eaters and consume food much faster than anticipated. The findings, based on high-resolution 3D simulations of accretion disks, revolutionize our understanding of the feeding habits of supermassive black holes.
The simulations depict the accretion disk surrounding a rotating black hole as a furious swirl of gas. As the gas orbits the black hole, distortions in spacetime caused by immense gravitational forces begin to tear the disk apart. Eventually, the disk fragments into inner and outer sub-disks. The black hole first devours the inner ring and then continues to feed as the remnants of the outer sub-disk spill inward to fill the void left by the consumed inner ring.
Previous studies suggested that one cycle of the eat-refill-eat process took hundreds of years to complete. However, the new simulations indicate that each cycle lasts only a few months. This rapid variation, according to lead researcher Nick Kaaz, could explain the drastic changes observed in quasars, which are highly luminous objects generated by black holes feeding off gas from their accretion disks.
Previous assumptions about the organization of accretion disks have also been challenged by the study. Scientists previously believed that the gas and particles within the disk rotated in the same plane and direction as the black hole’s rotation. However, the new simulations suggest that the regions surrounding the black hole are chaotic and turbulent.
Using the high-performance supercomputer Summit at Oak Ridge National Laboratory, the researchers conducted a 3D simulation of an inclined accretion disk, incorporating gas dynamics, magnetic fields, and general relativity. The rotation of a black hole influences the surrounding space, causing the entire disk to wobble like a gyroscope. The inner disk becomes increasingly tilted, resulting in collisions between gas from different regions. These collisions produce bright shocks that push the material toward the black hole.
The simulations also predict that the innermost part of the disk eventually separates from the rest due to the growing tilt. As a result, the sub-disks oscillate independently at different speeds and angles. The feeding process begins in the tearing region where the inner and outer sub-disks disconnect. Friction tries to hold the disk together, but the spacetime distortions from the black hole overpower it, causing collisions between the sub-disks. This collision leads to the inner disk being shaved off by the outer disk and pushed inward.
The study highlights the potential of these rapidly repeating eat-refill-eat cycles to explain the phenomenon of “variable-appearing” quasars. These quasars exhibit a pattern of turning on and off in a short period of time. Additionally, the simulations provide new insights into fundamental questions regarding feeding mechanisms and the properties of black holes.
Nicholas Kaaz, Matthew T. P. Liska, Jonatan Jacquemin-Ide et al. Nozzle Shocks, Disk Tearing, and Streamers Drive Rapid Accretion in 3D GRMHD Simulations of Warped Thin Disks. The Astrophysical Journal. DOI 10.3847/1538-4357/ace051