Outflow Launching Mechanisms

Abstract

Outflow from accretion flow seems to be quite general features of accretion processes. A number of launching mechanisms are known for accretion flow onto black holes: thermal wind, (continuum and line) radiation-pressure driven wind, and magnetically driven wind. To investigate the physics of outflow it is essential first to build good models for underlying accretion flow. Historically, various accretion disk models have been constructed under radially one-zone approximations, but they are not appropriate for exploring the outflow mechanisms, since the multi-dimensional motion of gas in accretion flow, including outflows, is totally neglected. Another limitation comes from that the disk viscosity, the most important ingredient, is described by the phenomenological α-viscosity model. We, here, elucidate the theory of accretion flow and associated outflow based on global, two-dimensional radiation-magnetohydrodynamic (radiation MHD) simulations, not relying on the α-viscosity prescription. We have succeeded in producing three distinct states of accretion flow by controlling only one parameter, a density normalization, and confirmed the occurrence of ubiquitous outflow from all the three states of accretion flow: supercritical, standard, and low-luminosity states. Especially strong outflow is confirmed from the supercritical and low-luminosity accretion flow. Several noteworthy features of the supercritical (or super-Eddington) accretion flows are found; that is, relativistic, collimated outflows (jets), and low-velocity, uncollimated outflows with clumpy structure.