3-DIMENSIONAL SIMULATIONS OF BLACK-HOLE TORI

Two- and three-dimensional numerical simulations are employed to investigate the global hydrodynamic nonaxisymmetric instabilities in thick, constant angular momentum (l) accretion gas tori in orbit around a Schwarzschild black hole. A radially slender torus proves to be violently unstable, evolving into a highly nonaxisymmetric orbiting fluid blob, or "planet," a result consistent with previous simulations of slender tori. A radially-wide torus develops an m = 1 nonaxisymmetric density perturbation near the pressure maximum and a trailing spiral wave that extends through the outer part of the torus. This global wave transports angular momentum through the torus, causing the average angular momentum distribution to evolve slowly away from l = constant. The unstable mode drives an accretion flow from the torus into the black hole. The role of accretion is further investigated by modeling a wide torus with an inner boundary at the cusp of the Schwarzschild effective potential. In such a torus, accretion is present throughout the evolution; only modest unstable mode growth is observed, and saturation occurs at low amplitude. An accretion flow is effective at terminating or preventing the growth of the instability in three-dimensional tori, suggesting the possibility of an instability-regulated mechanism for accretion from a thick torus. Comparison simulations performed in the torus equatorial plane show qualitative similarities between the two- and three-dimensional system, although the three-dimensional modes have a functional dependence on height z. The three-dimensional instabilities have lower perturbation amplitudes at mode saturation and are less effective at transporting angular momentum than the unstable modes in two-dimensional simulations. The nonaxisymmetric instabilities do not appear to be sufficiently robust to rule out the thick torus as a viable accretion disk model.