http://arxiv.org/abs/1603.04082
We present results of a set of three-dimensional, general relativistic radiation magnetohydro- dynamics simulations of thin accretion discs to test their thermal stability. We consider two cases, one that is initially radiation-pressure dominated and expected to be thermally unstable and another that is initially gas-pressure dominated and expected to remain stable. Indeed, we find that cooling dominates over heating in the radiation-pressure-dominated case, causing the disc to collapse vertically on the local cooling timescale. On the other hand, the gas-pressure- dominated case, which was run for twice as long as the radiation-pressure-dominated case, remains stable, with heating and cooling roughly in balance. Because the radiation-pressure- dominated disc collapses to the point that we are no longer able to resolve it, we had to terminate the simulation. Thus, we do not know for sure whether it might find a much thinner, stable solution or if it will make a transition to unstable expansion and exhibit limit-cycle be- havior. However, the fact that the cooling rate seems to be dropping faster than heating as the disc collapses suggests that the disc may be headed toward a stable, albeit thinner, solution. It is not clear, though, if the disc will remain radiation-pressure-dominated in that new state.
B. Mishra, P. Fragile, L. Johnson, et. al.
Tue, 15 Mar 16
68/77
Comments: 10 pages, 15 figures, submitted to MNRAS
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