A recent study led by researchers from Northwestern University has upended the astrophysical playbook on how supermassive black holes feed, revealing that these giants of the universe violently twist and rip apart space-time to consume matter at astonishingly rapid rates.
The discovery could help solve long-standing mysteries around phenomena like “changing-look” quasars, which abruptly flare up and then vanish without explanation and potentially challenge decades of accepted theories.
For years, the prevailing wisdom has posited that black holes “eat” gradually and orderly suck in matter at a glacial pace over tens of thousands of years. However, using high-resolution 3D simulations, researchers from Northwestern University painted a drastically different portrait.
According to this new study published on September 20 in The Astrophysical Journal, a supermassive black hole can complete one eating cycle in just a few months, indisposing previous estimates.
“Classical accretion disk theory predicts that the disk evolves slowly,” Nick Kaaz, a graduate student in astronomy at Northwestern’s Weinberg College of Arts and Sciences who led the study, said in a statement. “But some quasars — which result from black holes eating gas from their accretion disks — appear to drastically change over time scales of months to years.”
“This variation is so drastic. It looks like the inner part of the disk — where most of the light comes from — gets destroyed and then replenished. Classical accretion disk theory cannot explain this drastic variation. But the phenomena we see in our simulations potentially could explain this. The quick brightening and dimming are consistent with the inner regions of the disk being destroyed.”
The research team used Summit, one of the world’s largest supercomputers, located at Oak Ridge National Laboratory, to conduct a 3D general relativistic magnetohydrodynamics (GRMHD) simulation to explore how black holes gorge themselves ruthlessly.
The supercomputer allowed researchers to integrate gas dynamics, magnetic fields, and general relativity, providing a comprehensive view of black hole behavior and offering one of the highest-resolution simulations of accretion disks ever produced.
Through simulations, researchers discovered that black holes essentially “twist” the surrounding space-time, tearing apart the accretion disk—a violent whirlpool of gas that feeds them—into inner and outer sub-disks.
What happens next is an almost cinematic process of devour-refill-repeat. The black hole consumes the inner disk, and then debris from the outer sub-disk spills inward to fill the void, only to be devoured in turn.
“Black holes are extreme general relativistic objects that affect space-time around them,” Kaaz said. “So, when they rotate, they drag the space around them like a giant carousel and force it to rotate as well — a phenomenon called ‘frame-dragging.’ This creates a really strong effect close to the black hole that becomes increasingly weaker farther away.”
These fast cycles of “eat-refill-eat” potentially explain the baffling behavior of so-called “changing-look” quasars.
A quasar, short for “quasi-stellar radio source,” is a highly luminous galactic core powered by a supermassive black hole at the center of a galaxy. Emitting energy that can outshine an entire galaxy, quasars are among the brightest and most energetic objects in the universe, often visible across billions of light-years.
“Changing-look” quasars are a subset of quasars that display unusually rapid and drastic variations in their luminosity, seemingly switching on and off and undergoing significant changes in brightness or overall appearance. These changes occur over short periods, often in just a few months to a few years.
The erratic fluctuations of Changing-Look quasars have challenged conventional astrophysical theories, making them subjects of intense study as researchers seek to understand the mechanisms driving such dramatic shifts.
“The inner region of an accretion disk, where most of the brightness comes from, can totally disappear — really quickly over months,” Kaaz explained. “We basically see it go away entirely. The system stops being bright. Then, it brightens again, and the process repeats. Conventional theory doesn’t have any way to explain why it disappears in the first place, and it doesn’t explain how it refills so quickly.”
Some researchers have hypothesized that Changing-Look quasars could be stars that passed too close to a black hole and were torn apart. Others have suggested that the phenomena weren’t quasars but rather powerful supernovas.
Thanks to the recent high-resolution simulations, researchers believe the rapid disappearance and reappearance of Changing-Look quasars could be linked to the fast-changing inner region of their accretion disks.
According to Kaaz, simulations show that the region where the inner and outer sub-disks disconnect is where a black hole’s “feeding frenzy” truly begins.
“There is competition between the rotation of the black hole and the friction and pressure inside the disk,” Kaaz explained. “The tearing region is where the black hole wins. The inner and outer disks collide into each other. The outer disk shaves off layers of the inner disk, pushing it inwards.”
Traditional models often assume that accretion disks are orderly and aligned with the black hole’s rotation. However, Kaaz says recent simulations show this theory is likely incorrect.
“For decades, people made a very big assumption that accretion disks were aligned with the black hole’s rotation,” Kaaz said. “But the gas that feeds these black holes doesn’t necessarily know which way the black hole is rotating, so why would they automatically be aligned? Changing the alignment drastically changes the picture.”
Instead of moving uniformly, simulations show that inner and outer sub-disks independently wobble at different speeds and angles around a black hole.
The inner disks are prone to much faster oscillations than their outer counterparts. This disparity in rotational forces leads to a deforming or warping of the entire accretion disk.
Consequently, gas particles from disparate areas of the disk crash into each other, producing vivid bursts of light and energy. These high-energy collisions act as a propellant, thrusting material increasingly nearer to the gravitational pull of the black hole.
So rather than proportionately flowing towards the center of a black hole like water swirling down a drain, researchers say the independent sub-disks of a black hole wobble around like gyroscope wheels.
In addition to offering a better understanding of the feeding habits of black holes, researchers hope recent simulations will present tantalizing avenues for further investigations into the nature of these enigmatic titans, which possess the power to warp the very fabric of space-time.
In their concluding remarks, the researchers emphasized, “It is ultimately most important to be able to connect our results to observations, which can be accomplished by producing synthetic observations from simulation results such as those presented here.”
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com