Mass Outflows from Dissipative Shocks in Hot Accretion Flows

TL;DR

This paper investigates how dissipative shocks in hot accretion flows around black holes can produce outflows and jets, with the mass and energy loss fractions depending on black hole spin and flow parameters.

Contribution

It introduces a model of stationary shocks in Kerr accretion flows that explains the formation of outflows and quantifies mass and energy loss fractions.

Findings

Mass loss fraction varies from 0% to 95% depending on flow parameters.

Energy loss fraction is less than 1% for non-rotating black holes, higher for rotating ones.

Up to 50% of accreting mass can be diverted into outflows around rapidly rotating black holes.

Abstract

We consider stationary, axisymmetric hydrodynamic accretion flows in Kerr geometry. As a plausible means of efficiently separating a small population of nonthermal particles from the bulk accretion flows, we investigate the formation of standing dissipative shocks, i.e. shocks at which fraction of the energy, angular momentum and mass fluxes do not participate in the shock transition of the flow that accretes onto the compact object but are lost into collimated (jets) or uncollimated (winds) outflows. The mass loss fraction (at a shock front) is found to vary over a wide range (0 - 95%) depending on flow's angular momentum and energy. On the other hand, the associated energy loss fraction appears to be relatively low (<1%) for a flow onto a non-rotating black hole case, whereas the fraction could be an order of magnitude higher (<10%) for a flow onto a rapidly-rotating black hole. By estimating the escape velocity of the outflowing particles with a mass-accretion rate relevant for typical active galactic nuclei, we find that nearly 10% of the accreting mass could escape to form an outflow in a disk around a non-rotating black hole, while as much as 50% of the matter may contribute to outflows in a disk around a rapidly-rotating black hole. In the context of disk-jet paradigm, our model suggests that shock-driven outflows from accretion can occur in regions not too far from a central engine. Our results imply that a shock front under some conditions could serve as a plausible site where (nonthermal) seed particles of the outflows (jets/winds) are efficiently decoupled from bulk accretion.