Contrary to previous beliefs that black holes fed slowly, a group of researchers led by Northwestern University found that black holes consume matter much faster. They came to the conclusion using high-resolution 3D simulations.
DISK OF GAS
In these simulations, spinning black holes were found to twist the surrounding space-time, tearing apart the accretion disk of gas that encircles and feeds them. This process resulted in the formation of inner and outer sub disks. Remarkably, black holes first devoured the inner ring, and debris from the outer sub disk filled the gap, initiating a rapid and repetitive eat-refill-eat cycle.
BLACK HOLES; MATTER OF MONTHS
What’s truly astounding is that this entire cycle, which defies conventional wisdom, takes just a matter of months, a stark contrast to the centuries proposed by earlier research. This discovery has profound implications, shedding light on the behaviour of some of the brightest celestial objects, including quasars, which exhibit sudden, unexplained flares and disappearances.
Nick Kaaz, a graduate student in astronomy at Northwestern’s Weinberg College of Arts and Sciences, who led the study, remarked, “Classical accretion disk theory predicts that the disk evolves slowly, but some quasars change dramatically over months to years. This variation is so drastic that it appears like the inner part of the disk gets destroyed and then replenished.”
One key misconception that earlier researchers had was assuming that accretion disks aligned precisely with the black hole’s rotation. This new simulation, one of the most detailed to date, paints a different picture. It depicts the regions around black holes as turbulent and messy, far from the neat and orderly models previously conceived.
BALCK HOLES; THE METHOD
Using the powerful Summit supercomputer at Oak Ridge National Laboratory, the researchers executed a 3D general relativistic magnetohydrodynamics (GRMHD) simulation of a tilted accretion disk. This comprehensive model factored in gas dynamics, magnetic fields, and general relativity to provide a more accurate representation of black hole behaviour.
Kaaz explains, “Black holes drag space-time around them, forcing it to rotate—a phenomenon known as ‘frame-dragging.’ This creates a strong effect close to the black hole that becomes weaker farther away.” This frame-dragging effect causes the entire disk to wobble like a gyroscope, with the inner region wobbling more rapidly than the outer parts.
As the warping intensifies, the innermost part of the accretion disk eventually breaks away from the rest, leading to the independent motion of sub disks. Instead of moving together like a flat plate, the sub disks wobble at different speeds and angles, resembling the gyroscope’s wheels.
It’s at the point of this disconnection, where the inner and outer sub disks separate, that the feeding frenzy begins. While friction attempts to keep the disk intact, the black hole’s rotation, warping space-time, strives to tear it apart. This results in the collision of sub disks, creating bright shocks that drive material closer to the black hole.
In conclusion, these findings provide a plausible explanation for the enigmatic behaviour of “changing-look” quasars, which exhibit rapid fluctuations in brightness. This research also offers valuable insights into the feeding mechanisms of black holes, a central question in accretion-disk physics, with potential implications for understanding their longevity, brightness, and observational characteristics.