Jets from Time-Dependent Accretion Flows Onto a Black Hole

Abstract

We investigate time-dependent inviscid hydrodynamical accretion flows onto a black hole using numerical simulations. We consider the accretion that consists of hot tenuous gas with low specific angular momentum and cold dense gas with high specific angular momentum. The former accretes continuously and the latter highly intermittently as blobs. The high specific angular momentum gas blobs bounce at the centrifugal barrier and create shock waves. The low specific angular momentum gas is heated at the shock fronts and escapes along the rotation axis. The outgoing gas evolves into pressure-driven jets. Jet acceleration lasts until the shock waves fade out. The total amount of the mass ejection is about 1 − 11% of the mass of the blobs. The jet mass increases when the gas blobs are more massive or have larger specific angular momentum. We get narrower well-collimated jets when the hot continuous flow has a lower temperature. In the numerical simulations we used a finite difference code based on the total variation diminishing scheme. It is extended to include the blackbody radiation and to apply the multi time step scheme for time marching.

Non-axisymmetric instabilities in shocked adiabatic accretion flows

“…However, even with the simple inviscid hypothesis, the stability of the shock is not fully understood. In the isothermal limit, Nakayama (1992) introduced a global instability between a sonic point and a shock, and found the criterion that ‘post‐shock acceleration causes instability’, which was confirmed by the simulations of Nobuta & Hanawa (1994). Moreover, Nakayama (1994) investigated this instability in an adiabatic flow and claimed that such a criterion is also correct unless the shock is extremely strong.…”

Properties of accretion shock waves in viscous flows around black holes

“…Subsequently, Chakrabarti (1990b, hereafter C90b) showed that inclusion of viscosity reduces the region of the parameter space in that, at a sufficiently high viscosity, the Rankine–Hugoniot conditions which must be satisfied at a steady shock are not satisfied anywhere in the flow. The existence of standing shocks in sub‐Keplerian inviscid accretion discs has been tested independently by several groups since then (Nobuta & Hanawa 1994; Yang & Kafatos 1995; Lu & Yuan 1997). Numerical simulations have also been carried out with several independent codes such as smoothed particle hydrodynamics (SPH) and total variation diminishing (TVD) and distinct standing shocks were found exactly at the predicted locations (Chakrabarti & Molteni 1993; Molteni, Ryu & Chakrabarti 1996b).…”

Outflow rates in a black hole environment in presence of a dissipative standing shock

“…As the flow moves closer to the black hole, and the centrifugal force grows, at some point, the supersonic flow may become subsonic at the shock front (C89; Nobuta & Hanawa 1994). It becomes supersonic again after passing through the inner critical point (C89).…”