According to new high-resolution 3D simulations, spinning black holes twist space-time around them, eventually ripping apart the violent maelstrom of gas (or accretion disk) that surrounds and nourishes them. This results in the disc being torn into inner and outer sub-discs. The black hole swallows the inner ring first. Debris from the outer subdisc then flows into the inner to fill the space left by the consumed inner ring, and the consumption process repeats. An endlessly repeating cycle of eating-eating-eating takes just a few months – an incredibly fast time frame compared to the hundreds of years previously suggested by researchers. This new discovery could help explain the spectacular behavior of some of the brightest objects in the night sky, including quasars, which flare up suddenly and then disappear without explanation.
“Classical accretion disk theory predicts that the disk evolves slowly,” said Nick Kaaz of Northwestern, who led the study. “But some quasars – caused by black holes feeding on gas from their accretion disks – appear to change significantly over months or even years. This transformation is very drastic. It appears that the inside of the dish – where most of the light comes from – was destroyed and then reassembled. The classical theory of accretion disks cannot explain this drastic change. But the phenomenon observed in our simulation can explain this. The rapid brightening and fading are consistent with destruction of the inner regions of the disc. Kaaz is a graduate student in astronomy in Northwestern’s Weinberg College of Arts and Sciences and a member of the Center for Interdisciplinary Research and Exploration in Astrophysics (CIERA). Kaaz was advised by paper co-author Alexander Tchekhovskoy, associate professor of physics and astronomy at Weinberg and a member of CIERA.
Accretion disks around black holes are physically complex objects, making them extremely difficult to model. Conventional theories have tried to explain why these disks glow brightly and then suddenly dim, sometimes to the point of disappearing altogether. Previous researchers have mistakenly assumed that accretion disks are relatively ordered. In these models, gas and particles swirl around the black hole – in the same plane as the black hole and in the same direction of the black hole’s rotation. Then, over a period of hundreds to several hundred thousand years, gas particles gradually rush into the black hole to feed it. “For decades, it was thought that accretion disks were aligned with the rotation of the black hole,” Kaaz said. “But the gas that fuels these black holes doesn’t necessarily know which direction the black hole is spinning, so why are they automatically aligned? Changing the alignment will completely change the image.
The researchers’ simulations, one of the highest resolution of an accretion disk to date, indicate that the regions surrounding black holes are far more turbulent and chaotic places than previously thought. think before. More like a gyroscope, less like a disk Using Summit, one of the world’s largest supercomputers located at Oak Ridge National Laboratory, researchers performed 3D simulations of general relativistic magnetohydrodynamics (GRMHD) of an accretion disk. thin, inclined capacitor. While previous simulations were not powerful enough to include all the physics needed to construct a realistic black hole, the Northwestern-led model includes gas dynamics, magnetic fields and relativity. contrast to paint a more comprehensive picture. “Black holes are relatively large objects that affect the space-time around them,” Kaaz said. “So, as they spin, they pull on the surrounding space like a giant conveyor belt and force it to spin as well – a phenomenon called ‘frame dragging’. This creates a very strong effect near the black hole and getting weaker and weaker.”
Shifting the frame causes the entire disk to oscillate in a circle, similar to how a gyroscope moves before it. But the inner disk wants to oscillate much faster than the outer parts. This force mismatch causes the entire disk to deform, causing gases from different parts of the disk to collide. Collisions create shocks of light that bring matter violently close to the black hole. As the deformation increases, the innermost region of the accretion disk continues to oscillate faster and faster until it separates from the rest of the disk. Then, according to the new simulation, the daughter disks began to grow independently of each other. Instead of moving smoothly like a flat sheet surrounding the black hole, the disks wobble independently at different speeds and angles, like the wheels of a gyroscope. “When the inner disc is torn, it functions independently before,” says Kaaz. “It moves faster because it is closer to the black hole and because it is small it is easier to move.”
“Where black holes win” According to the new simulation, the tear zone – where the inner and outer subdiscs become disconnected – is where the crazy appetite really begins. While friction tries to hold the disk together, the twisting of space-time caused by the spinning black hole wants to tear it apart. “There is competition between the black hole’s rotation and the friction and pressure inside the disk,” Kaaz said. “The tear region is where the black hole wins. The inner and outer discs collide. The outer disc scrapes away the layers of the inner disc, pushing it inwards. Now the subdisks intersect at different angles. The outer disc pours material into the inner disc. This extra mass also pushes the inner disk toward the black hole, where it is swallowed. The black hole’s gravity will then pull gas from the outer region into the now empty inner region to fill it.
These rapid eating-eating-eating cycles likely explain so-called “appearance-changing” quasars, Kaaz said. Quasars are extremely bright objects, emitting 1,000 times more energy than the 200 to 400 billion stars in the Milky Way. Quasars change their appearance to be even more extreme. They appear to turn on and off over a period of months – a very small time period for a typical quasar. Although classical theory has hypothesized how quickly accretion disks grow and change brightness, observations of quasars changing appearance show that they actually evolve rapidly much more. “The inner region of the accretion disk, where most of the luminosity is emitted, can disappear completely – very quickly within a few months,” Kaaz said. “We’re basically seeing this completely disappear. The system stops lighting. Then it deletes again and the process repeats. Conventional theory has no way of explaining why it disappeared in the first place, nor does it explain why it filled up so quickly. » The new simulations could not only explain quasars but could also answer current questions about the mysterious nature of black holes.
source: https://arxiv.org/abs/2210.10053