Convection‐dominated Accretion Flows

Abstract

Nonradiating advection-dominated accretion Ñows are convectively unstable in the radial direction. We calculate the two-dimensional (r-h) structure of such Ñows assuming that (1) convection transports angular momentum inward, opposite to normal viscosity, and (2) viscous transport by other mechanisms (e.g., magnetic Ðelds) is weak (a > 1). Under such conditions convection dominates the dynamics of the accretion Ñow and leads to a steady state structure that is marginally stable to convection. We show that the marginally stable Ñow has a constant temperature and rotational velocity on spherical shells, a net Ñux of energy from small to large radii, zero net accretion rate, and a radial density proÐle of o P r~1@2, Ñatter than the o P r~3@2 proÐle characteristic of spherical accretion Ñows. This solution accurately describes the full two-dimensional structure of recent axisymmetric numerical simulations of advection-dominated accretion Ñows.