Escape conditions of radiative-driven strati from luminous accretion disks

Abstract

Abstract We examine the dynamical motion and escape conditions of continuum-driven strati (flat cloud) with finite optical depth from luminous accretion disks around a black hole. We adopt the near-disk approximation, and treat the problem in the framework of special relativity, where the radiation drag force as well as the radiation pressure are included. We find that the optically thin strati are easy to accelerate, compared with the particles, and the escape condition of the stratus is reduced. That is, when the disk luminosity is around the Eddington luminosity, the optically thin strati can escape from the inner disk (≲ 20 rg; rg being the Schwarzschild radius). When the disk luminosity is about half the Eddington luminosity, it can escape at around 5 rg. This is due to the translucent effect. In addition, the trajectories of the strati are not vertical, but a funnel-like shape due to the centrifugal force. Stratus outflow could easily blow out from usual accretion disks with sub-Eddington luminosities, and this may explain outflows observed in broad absorption line quasars and ultra-fast outflow objects.