A magnetohydrodynamic nonradiative accretion flow in three dimensions

We present a global magnetohydrodynamic (MHD) three-dimensional simulation of a nonradiative accretion flow originating in a pressure-supported torus. The evolution is controlled by the magnetorotational instability, which pr oduces turbulence. The flow forms a nearly Keplerian disk. The total pressu re scale height in this disk is comparable to the vertical size of the init ial torus. Gas pressure dominates near the equator; magnetic pressure is mo re important in the surrounding atmosphere. A magnetically dominated bound outflow is driven from the disk. The accretion rate through the disk exceed s the final rate into the hole, and a hot torus forms inside 10r(g). Hot ga s, pushed up against the centrifugal barrier and confined by magnetic press ure, is ejected in a narrow, unbound, conical outflow. The dynamics are con trolled by magnetic turbulence, not thermal convection, and a hydrodynamic alpha -model is inadequate to describe the flow. The limitations of two-dim ensional MHD simulations are also discussed.