Simulations of accretion flows crossing the last stable orbit

We use three-dimensional magnetohydrodynamic simulations, in a pseudo-Newto nian potential, to study geometrically thin accretion disk flows crossing r (ms), the marginally stable circular orbit around black holes. We concentra te on vertically unstratified and isothermal disk models but also consider a model that includes stratification. In all cases we find that the sonic p oint lies just inside r(ms), with a modest increase in the importance of ma gnetic field energy, relative to the thermal energy, observed inside the la st stable orbit. The time-averaged gradient of the specific angular momentu m of the flow, (dl/dr), is close to zero within r(ms) despite the presence of large fluctuations and continuing magnetic stress in the plunging region . The result that the speciDc angular momentum is constant within r(ms) is in general agreement with traditional disk models computed using a zero-tor que boundary condition at the last stable orbit.