Quasi-Spherical, Time-Dependent Viscous Accretion Flow: One-Dimensional Results

Abstract

We investigated the instability of advective accretion flow as a consequence of angular momentum transfer in one-dimensional, quasi-spherical transonic accretion flow around a non-rotating black hole. The code is designed to include the effects of viscosity; the hydrodynamics component preserves angular momentum strictly with Lagrangian and remap method in absence of viscosity, while the viscosity component updates viscous angular momentum transfer through the implicit method. We performed two tests to demonstrate the suitability of the code for accretion study. First, we simulated the inviscid, low angular momentum, transonic accretion flow with shocks around a black hole, and then the subsonic, self-similar ADAF solution around a Newtonian object. Both simulations fitted the corresponding analytical curves extremely well. We then simulated a rotating, viscous, transonic fluid with shocks. We showed that for low viscosity parameter, stable shocks at larger distance are possible. For higher viscosity parameter, more efficient angular momentum transfer in the post-shock disk makes the shock structure oscillatory. Moreover, as the shock drifts to larger distances, a secondary inner shock develops. We showed that the inner shock is the direct consequence of expansion of the outer shock, as well as creation of regions with ∂l/∂r < 0 due to more efficient angular momentum transfer near the inner sonic point. We showed that all disk parameters, including emissivity, oscillate with the same period as that of the shock oscillation. Our simulation may have implication for low frequency QPOs, e.g., GRO J1655-40 and XTE J1550-564.

Estimation of mass outflow rates from viscous relativistic accretion discs around black holes

“…2006) tells us that the essential physics around super-massive and stellar mass BHs are similar. Aktar et al 2015), dissipative flow (Das 2007;, and has also been confirmed in simulations (Molteni et al 1996b;Lee et al 2011;Das et al 2014). The post-shock region of the disc (PSD), has some special properties.…”

Periodic mass loss from viscous accretion flows around black holes

“…In realistic disc, both processes are active, and both should produce shock oscillation. Interestingly though, viscosity can produce multiple shocks (for one spatial dimensional results see Lee et al 2011), while no such thing has been reported with cooling processes, albeit investigations with cooling processes have not been done extensively. We would like to investigate the combined effect of cooling and viscous dissipation in future, to ascertain the viability of 'shock cascade' in much greater detail.…”

“…We would like to find the condition of the shocked disc that produces weak or strong jets. Disc instability due to viscous transport has been shown before and has been identified with QPOs (Lanzafame et al 1998(Lanzafame et al , 2008Lee et al 2011), however, we would like to show how this instability might affect the shock induced bipolar outflows. Moreover, it has been shown theoretically that the energy and angular momentum for which steady shock exists in inviscid flow, will become unstable for viscous flow (Chakrabarti & Das 2004;.…”

Viscosity parameter in dissipative accretion flows with mass outflow around black holes

“…This difference induces major changes in the Rankine-Hugoniot conditions, though, some of their conclusions remain similar to those present in our work. In Lanzafame et al (1998) and Lee et al (2011) shocks move outward with increasing α as in our present paper where we kept the conditions on the horizon and inner sonic points fixed.…”