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Feature - Flip-flopping of black hole accretion disks scrutinized

Feature - Flip-flopping of black hole accretion disks scrutinized

Clues to an astrophysical mystery from Renaissance Computing Institute on Vimeo.

Do whirlpools of gas flip-flop as they are sucked into black holes? According to a new simulation powered by TeraGrid, the answer is “Yes.”

The accretion disk of a black hole forms from gas attracted by the black hole’s massive gravitational pull. For the last 20 years, astrophysicists have debated whether the whirlpool-like motion of the accretion disk will periodically reverse motion, a behavior called ‘flip-flop.’

When flip-flopping first turned up in a 1988 numerical simulation, some scientists argued that it explains recurrent x-ray flares observed by the European X-Ray Observatory in 1985. But in subsequent years, although some simulations showed flip-flop, others did not, casting doubt on the existence of the phenomenon.

“The earlier work was criticized for a wide variety of reasons, but I think the chief among them was the lack of computer power and hence accuracy of the computation,” said John Blondin, a physics researcher at North Carolina State University.

Blondin and T. Chris Pope, an undergraduate student in North Carolina State University’s Physics Department, wanted to settle the matter once and for all. That meant getting more computing power. To do so, they joined forces with the Texas Advanced Computing Center and TeraGrid.

Their simulation found that the accretion disk reversed direction repeatedly, confirming that at least in this model of black hole accretion disks, flip-flop does occur. In order to better demonstrate the flip-flop phenomenon, Blondin and Pope asked Renaissance Computing Institute animator Steve Chall to create a movie from the simulation.

“This problem has been around forever, and what we were able to do with really big computers was to do it right,” said Blondin. The most basic form of the equation used in the simulation was originally formulated by Fred Hoyle and Ray Lyttleton in 1939. Blondin added, “It was fun to be employing supercomputers to solve a problem from 1939.”

—Miriam Boon, iSGTW

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