Physics of Accretion Disks Around Black Holes

Johns Hopkins University, Baltimore MD

Investigators

Abstract

AST 0205806 Krolik Black holes are tremendously powerful sources of light. In aggregate, the total light power produced by black holes in the Universe is almost as much as that generated by stars. However, the mechanism by which black holes are able to radiate so much light has remained mysterious for many years. The fundamental reason for this mystery is that, without friction, matter in orbit around a massive object would go round and round forever, and no energy would be released at all. Except for the region immediately outside its edge, this rule is as true for a black hole as for an ordinary object. Because friction caused by ordinary viscosity is far too weak to account for the observed rate at which mass is swallowed by black holes; the source of this friction had been a mystery for decades. During the 1990s, however, we gradually gained confidence in what was once the speculative suggestion that tangled magnetic fields would spontaneously grow in strength in accreting matter, and the forces they create would be strong enough to provide the necessary "friction". Since calculations of tangled magnetic field forces are very complex they must be done with large computer simulations. This project will conduct a coherent program of large-scale numerical simulations with a pair of goals: a) to compute how the magnetic forces control the total amount of energy released in black hole accretion; and b) to show how the released energy finds its way into heat, and then the light that we see. ***