Supermassive black holes are giants between millions and billions of times heavier than our sun that reside at the centers of most galaxies in our universe, including our own. Milky Way — and they are best known by the brilliant disks of gas that orbit them. These discs are the remains of ill-fated stars that were once torn apart and trapped by black holes, which are actually fed by these discs themselves. However, scientists still aren’t sure how, exactly, black holes celebrate.
For example, astrophysicists have puzzled for decades about why the material that is engulfed by black hole it does not immediately fall into its abyss. Instead, they all come together to form and hold a hot, rapidly spinning disk that then spirals toward the black hole. And, in the process, the disk radiates brightly as it converts gravitational energy into heat. The disc is the main source of light from a black hole, and it hovers as long as there is material nearby to absorb the void.
A new computer simulation suggests that this prolonged existence of accretion disks may owe itself to the fact that each disk is almost completely controlled by the magnetic fields of the corresponding black hole. It is possible that these fields drive the gas into a disk. Scientists say that the simulation, which, for the first timetracing the journey of pristine gas from the early universe to the point at which it ends up in the accretion disk of a supermassive black hole could help them fine-tune their predictions about different aspects of accretion disks, including their masses and thicknesses and the rate of fall of the material.
“Our theories told us that discs should be flat like pancakes,” said Phil Hopkins, a theoretical astrophysicist at the California Institute of Technology. STATEMENT. “But we knew that wasn’t right, because astronomical observations reveal that the discs are actually fluffy – more like an angel cake. Our simulation helped us understand that the magnetic fields are supporting the disc material, making the fluffier one.”
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Hopkins and his team did what they describe as a “super zoom” in a virtual supermassive black hole. To virtually replicate the dynamics of a black hole, researchers provide information about the physics of various cosmic phenomena on galactic scales. These included the governing equations gravity, dark matter AND dark energy – the latter are intangible substances that make up most 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 code that could simply 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 UNIVERSE, and STARFORGE, which examines small-scale structures, allowed the team to create a simulation whose resolution is a thousand times better than its predecessor, according to the university’s statement. “We built it in a very modular way, so you could roll in and take out any part of the physics you wanted for a particular problem, but they were all 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 passes through a complex tangle of merged galaxies before zooming into an active supermassive black hole, or quasarsurrounded by an accretion disk, which appears to be feeding gas into the black hole at speeds comparable to the brightest known quasars in our universe.
The magnetic fields can be seen to remove momentum from the disk, which frees the material to spin inward until it reaches the event horizon or the “surface” of the black hole, where 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 just seen that accretion disk, but what was very surprising was that the simulated disk does not look like what we have thought for decades it should look like.”
The findings are described in a paper published in March in The Open Journal of Astrophysics.