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Gluttonous Black Holes Eat Faster Than Thought. Does That Explain Quasars?

At the heart of large galaxies like our Milky Way, there resides a supermassive black hole (SMBH.) These behemoths draw stars, gas, and dust toward them with their irresistible gravitational pull. When they consume this material, there’s a bright flare of energy, the brightest of which are quasars.

While astrophysicists think that SMBHs eat too slowly to cause a particular type of quasar, new research suggests otherwise.

The research is published in The Astrophysical Journal, and the title is “Nozzle Shocks, Disk Tearing, and Streamers Drive Rapid Accretion in 3D GRMHD Simulations of Warped Thin Disks.” The lead author is Nick Kaaz, a graduate student in astronomy at Northwestern University.

The new research is based on computer simulations called 3D general relativistic magnetohydrodynamics (GRMHD) simulations. A powerful supercomputer called Summit, one of the world’s fastest computers and a 340-ton behemoth itself, carried out the simulations at the Oak Ridge National Laboratory.

“It looks like the inner part of the disk — where most of the light comes from — gets destroyed and then replenished.”

Nick Kaaz, lead author, Northwestern University

When SMBHs draw material toward themselves, the material doesn’t fall directly into the hole. Instead, it forms an accretion disk, a whirling disk of gas and dust. The rotating disk of material heats up and gives off electromagnetic energy that we can see with different telescopes when it falls into the black hole. When they’re extremely luminous, they’re called quasars.

This artist's impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. When black holes consume a lot of disc material quickly, it can cause a quasar. Credit: ESO, ESA/Hubble, M. Kornmesser
This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disk. When black holes consume a lot of disk material quickly, it can cause a quasar. Credit: ESO, ESA/Hubble, M. Kornmesser

But these disks are very difficult to study. They’re extremely complicated. Sometimes they flare brightly and then suddenly grow dimmer, on timescales of mere months, which is an extraordinarily short period of time for an astrophysical object. Current theory can’t explain it.

The new simulations show that SMBHs eat faster than thought. The encounter between the disk and the hole is violent and tears the whirlpool of gas into two pieces, an inner sub-disk and an outer sub-disk.


The Summit supercomputer simulations show that a black hole’s accretion disk is torn into two sub-disks and the black hole eats the inner disk quickly, creating a short-lived quasar. Image Credit: Kaaz et al. 2023.

The SMBH consumes the inner sub-disk first. It takes only a matter of months for the black hole to consume this inner ring of swirling dust, and as it does so, it releases an enormous amount of energy as a quasar. Then material from the outer disk moves inward forming a new inner disk, and the entire process repeats.

If the simulations are correct, and this eat, refill, eat cycle takes mere months, instead of hundreds of years, then it can explain some observed quasars that last only a few months. There are
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