Simulation of thick accretion disks with standing shocks by smoothed particle hydrodynamics

Abstract

We present results of numerical simulation of inviscid thick accretion disks and wind flows around black holes. We use Smoothed Particle Hydrodynamics (SPH) technique for this purpose. Formation of thick disks are found to be preceded by shock waves travelling away from the centrifugal barrier. For a large range of the parameter space, the travelling shock settles at a distance close to the location obtained by a one-and-a-half dimensional model of inviscid accretion disks. Occasionally, it is observed that accretion processes are aided by the formation of oblique shock waves, particularly in the initial transient phase. The post-shock region (where infall velocity suddenly becomes very small) resembles that of the usual model of thick accretion disk discussed in the literature, though they have considerable turbulence. The flow subsequently becomes supersonic before falling into the black hole. In a large number of cases which we simulate, we find the formation of strong winds which are hot and subsonic when originated from the disk surface very close to the black hole but become supersonic within a few tens of the Schwarzschild radius of the blackhole. In the case of accretion of high angular momentum flow, very little amount of matter is accreted directly onto the black hole. Most of the matter is, however, first squeezed to a small volume close to the black hole, and subsequently expands and is expelled as a strong wind. It is quite possible that this expulsion of matter and the formation of cosmic radio jets is aided by the shock heating in the inner parts of the accretion disks.

Estimation of bipolar jets from accretion discs around Kerr black holes

“…It has been shown previously that accretion disc shock may launch bipolar jets (Molteni et al 1994(Molteni et al , 1996aDas et al 2014;Lee et al 2016). The jump condition across an accretion shock is obtained by conserving fluxes across the shock front, e.g., mass flux, momentum flux and energy flux (Taub 1948).…”

Standing Shock Instability in Advection-Dominated Accretion Flows

“…The studies of nonspherical accretion flows that include angular momentum have demonstrated the variety and complexity of structures forming around the central object(e.g., Hawley et al 1984aHawley et al , 1984bEggum et al 1985Eggum et al , 1987Eggum et al , 1988Chakrabarti 1989;Chakrabarti & Molteni 1993;Molteni et al 1994). Chakrabarti (1989) performed a detailed study of the structure of vertically hydrostatic, inviscid, adiabatic, steady accretion flows with Rankine-Hugoniot, isentropic, and isothermal standing shock waves.…”

Periodic mass loss from viscous accretion flows around black holes

“…Hot electrons in the post-shock region, abbreviated as CENBOL (CENtrifugal pressure supported Boundary Layer), may explain the power-law tail of the spectrum from black hole candidates in hard states, while a weak or no shock solution produces a dearth of hot electrons which may cause the weaker power-law tail in the soft states (Chakrabarti & Titarchuk 1995;Mandal & Chakrabarti 2010). Moreover, a large number of authors have shown the formation of bipolar outflows from the post-shock accretion flow, both numerically (Molteni et al 1994(Molteni et al , 1996b as well as analytically (Le & Becker 2005;Chattopadhyay & Das 2007;Fukumura & Kazanas 2007;Das & Chattopadhyay 2008;Das et al 2009;Kumar et al , 2014. It is also interesting to note that, by considering a simplified inviscid accretion, and which has the right parameters to form a standing shock, Das et al (2001) qualitatively showed that there would be no jets in no-shock or weak shock condition of the disc, or in other words, when the disc is in the soft spectral state.…”