Astronomers from NASA, Johns Hopkins University and the Rochester Institute of Technology used 960 of the Ranger supercomputer's nearly 63,000 central processing units over 27 days to confirm long-held suspicions about how gas behaves around a black hole.
"Our work traces the complex motions, particle interactions and turbulent magnetic fields in billion-degree gas on the threshold of a black hole, one of the most extreme physical environments in the universe," said lead researcher Jeremy Schnittman, an astrophysicist at NASA's Goddard Space Flight Center.
Gas sucked in towards a black hole first orbits around it and then accumulates into a sort of flattened disc before spiralling in, getting more and more compressed and heated as it nears the centre. The temperature of this compressed gas eventually reaches up to 20 million degrees Fahrenheit (12 million °C), around 2,000 times hotter than the surface of the Sun, and shines brightly in low-energy, or soft, X-rays.
However, observations also show that black holes shine with large amounts of hard X-rays, lighting up to hundreds of times brighter than soft X-rays, implying that even hotter gas at temperatures of billions of degrees is present.
Using the Ranger supercomputer at the Texas Advance Computing Centre in the University of Texas, the boffins modelled the environment and showed that both types of X-rays come from gas spiralling in toward the black hole. The rising temperature, density and speed of the gas being sucked into the event horizon* dramatically amplifies magnetic fields in the disc, which then put even more pressure on the gas.
The result is a corona of gas whipping around the black hole at speeds approaching the speed of light in a structure similar to the corona around the Sun, as predicted by astronomers.
"Black holes are truly exotic, with extraordinarily high temperatures, incredibly rapid motions and gravity exhibiting the full weirdness of general relativity," John Hopkins' Julian Krolik said. "But our calculations show we can understand a lot about them using only standard physics principles."
The study was based on a non-rotating black hole but the models are now being extended to spinning ones, where rotation pulls the inner edge of the disc further inward and conditions are even more extreme.
The paper, "X-ray Spectra from MHD Simulations of Accreting Black Holes", published in The Astrophysical Journal, is available on arXiv here. ®
* As described by NASA boffins: "The event horizon is the boundary where all trajectories, including those of light, must go inward. Nothing, not even light, can pass outward across the event horizon and escape the black hole."
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