Abstract
Both HD and MHD numerical simulations of hot accretion flows have indicated that the inflow accretion rate decreases inward. Two models have been proposed to explain this result. In the adiabatic inflow–outflow solution (ADIOS), this is because of the loss of gas in the outflow. In the alternative convection-dominated accretion flow model, it is thought that the flow is convectively unstable and gas is locked in convective eddies. We investigate the nature of the inward decrease of the accretion rate using HD and MHD simulations. We calculate various properties of the inflow and outflow such as temperature and rotational velocity. Systematic and significant differences are found. These results suggest that the inflow and outflow are not simply convective turbulence; instead, systematic inward and outward motion (i.e., real outflow) must exist. We have also analyzed the convective stability of MHD accretion flows and found that they are stable. These results favor the ADIOS scenario. We suggest that the mechanisms of producing outflow in HD and MHD flows are the buoyancy associated with the convection and the centrifugal force associated with the angular momentum transport mediated by the magnetic field, respectively. The latter is similar to the Blandford & Payne mechanism but no large-scale open magnetic field is required. We discuss one observational application, namely the formation of the Fermi bubbles in the Galactic center.
Coffee and tea will be served 20 minutes prior to the seminar.