Black holes are faster eaters than previously believed, study says

(CN) — A new study led by researchers from Northwestern University reveals that the speed at which black holes eat surrounding matter is magnitudes faster than traditional models had shown.

Black holes are astronomical objects with gravitational pulls so strong that nothing, not even light, can escape once pulled in. This consumption process has been further illuminated by a study published on Wednesday in The Astrophysical Journal.

Nick Kaaz, of Northwestern’s Weinberg College of Arts and Science, led the study and performed the research using the Summit supercomputer located at the Oak Ridge National Laboratory in Tennessee.

The study involved examining accretion disks, which form around massive celestial bodies like black holes or stars, and are made of gas, plasma, dust and other particles.

“Classical accretion disk theory predicts that the disk evolves slowly,” Kaaz said in a statement.

Kaaz performed high-resolution 3D simulations that show that spinning black holes cause the accretion disks to wobble and split into an inner and outer piece.

The research found that once the accretion disks separate, the inner disk is consumed first by the black hole and debris from the outer disk is brought inward to fill the gap left by the inner ring, in an endless “eat-refill-eat” process.

The complexity of these disks makes them difficult for scientists to model and why using the Summit supercomputer was essential because it allowed the inclusion of gas dynamics, magnetic fields and general relativity to model a more realistic black hole.

The increased speed at which the disks are consumed may also help explain other observable behaviors, such as the way they move.

“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.”

Kaaz also believes that the detailed eat-refill-eat cycle could possibly explain why some quasars have appeared to go from bright to dim in a few short months.

Quasars or quasi-stellar objects are believed to be powered by supermassive black holes and emit more than 1,000 times the energy than all the stars that make up the Milky Way.

“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,” Kaaz said. “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.”

Kaaz hopes that this research can help answer more of the many ongoing questions about the nature of black holes.

“How gas gets to a black hole to feed it is the central question in accretion-disk physics,” Kaaz said. “If you know how that happens, it will tell you how long the disk lasts, how bright it is and what the light should look like when we observe it with telescopes.”

Kaaz was advised by the paper’s co-author Alexander Tchekhovskoy, an associate professor of physics at Weinberg. The research was supported by the U.S. Department of Energy and National Space Foundation.

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