Supermassive black holes are giants millions to billions of times more massive than our Sun that reside at the centers of most galaxies in our universe, including our own. Milky Way — and they are best known for the brilliant disks of gas that swirl around them. These disks are the remains of ill-fated stars that were once torn apart and captured by the black holes, which actually feed on the disks themselves. Yet scientists still don’t know exactly how black holes do their feeding.
For example, astrophysicists have puzzled for decades over why material dragged along by the sun black hole doesn’t fall straight into its abyss. Instead, everything comes together to form and sustain a hot, rapidly spinning disk that then spirals toward the black hole. And in the process, the disk shines brilliantly as gravitational energy is converted into heat. The disk is the black hole’s main source of light, and it floats as long as there is material nearby to suck up the void.
A new computer simulation suggests that this long-lasting existence of accretion disks may be due to the fact that each disk is driven almost entirely by the magnetic fields of its respective black hole. It is possible that these fields steer the gas into disk shapes. Scientists say the simulation, which is the first to timewhich has followed the journey of pristine gas from the early universe to the point where it falls into the accretion disk of a supermassive black hole, can help them fine-tune their predictions about several aspects of accretion disks, including their masses, thicknesses and the rates at which material falls into them.
“Our theories told us the disks should be flat like crepes,” said Phil Hopkins, a theoretical astrophysicist at the California Institute of Technology in a rack“But we knew this wasn’t right, because astronomical observations show that the disks are actually fluffy — more like angel food cake. Our simulation helped us understand that magnetic fields are holding the disk material up, making it fluffier.”
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Hopkins and his team performed what they describe as a “super zoom-in” on one virtual supermassive black hole. To virtually replicate the black hole’s dynamics, the researchers input information about the physics of various cosmic phenomena on a galactic scale. These included equations that gravity, dark matter And dark energy —the latter of which are intangible substances which form the greater part of the contents of the universe—as well as stars and galaxies. Creating such a simulation was not only a computational challenge, but also one that required a code that could easily handle all the complex physics, the researchers say.
A culmination of two major collaborations at Caltech, called FIRE, which focuses on large-scale structures in the universeand STARFORGE, which studies small-scale structures, allowed the team to create a simulation that is 1,000 times more resolving than its predecessor, the university statement said. “We built it in a very modular way, so that you could turn on and off any bit of physics you wanted for a particular problem, but they were all cross-compatible,” Hopkins said.
Using that code, the researchers simulated a black hole 10 million times more massive than our sun, starting in the early universe. The simulation then flies through a complex tangle of merging galaxies before zooming in on an active supermassive black hole, or quasarssurrounded by an accretion disk, which feeds gas toward the black hole at a rate comparable to that of the brightest known quasars in our universe.
Magnetic fields are seen to remove momentum from the disk, leaving the material free to spiral inward until it reaches the event horizon or the “surface” of the black hole, from which it cannot escape.
“In our simulation, we see this accretion disk forming around the black hole,” Hopkins said in the statement. “We would have been very excited if we had actually seen that accretion disk, but what was very surprising was that the simulated disk does not look like what we have thought it should look like for decades.”
The findings are described in a paper published in March in The Open Journal of Astrophysics.