Properties of accretion shock waves in viscous flows around black holes

Abstract

Accretion flows having low angular momentum and low viscosity can have standing shock waves. These shocks arise because of the presence of multiple sonic points in the flow. We study the region of the parameter space in which multiple sonic points occur in viscous flows in the absence of cooling. We also separate the parameter space into regions allowing steady shocks and oscillating shocks. We quantify the nature of two critical viscosities which separate the flow topologies. The post‐shock region being hotter, it emits harder X‐rays and oscillating shocks cause oscillating X‐ray intensities giving rise to quasi‐periodic oscillations. We show that with the increase in viscosity parameter, the shock always moves closer to the black hole. This implies an enhancement of the quasi‐periodic oscillation frequency as viscosity is increased.

The role of viscosity in AGN outflows in relation to jet periodicities

“…Physical viscosity, combined together with the angular momentum, produces a shock front capable of pushing out part of the accreting flow from the disc. For low viscosity values, the subsonic post-shock region, close to the BH, develops in a radially, more-extended zone where the higher the viscosity the farther the steady shock front where the RH jump conditions are satisfied (Lanzafame et al 1998;Chakrabarti & Das 2004). Such a result has been pointed out in Chakrabarti & Molteni (1995), Lanzafame et al (1998), and in Chakrabarti & Das (2004).…”

“…Such a result has been pointed out in Chakrabarti & Molteni (1995), Lanzafame et al (1998), and in Chakrabarti & Das (2004). Moreover, Lanzafame et al (1998), and Chakrabarti & Das (2004), have shown that, when the Article published by EDP Sciences RH condition is not satisfied, the shock front shows a periodical behaviour instead of a stationary one.…”

“…For low viscosity values, the subsonic post-shock region, close to the BH, develops in a radially, more-extended zone where the higher the viscosity the farther the steady shock front where the RH jump conditions are satisfied (Lanzafame et al 1998;Chakrabarti & Das 2004). Such a result has been pointed out in Chakrabarti & Molteni (1995), Lanzafame et al (1998), and in Chakrabarti & Das (2004). Moreover, Lanzafame et al (1998), and Chakrabarti & Das (2004), have shown that, when the Article published by EDP Sciences RH condition is not satisfied, the shock front shows a periodical behaviour instead of a stationary one.…”

Periodic mass loss from viscous accretion flows around black holes

“…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;. We would like to see how the mass outflow rate depend on unstable shock, or in other words, if there is any connection between QPOs and mass outflow rate.…”

“…In this paper, we will focus on the oscillation of the shock front, but now due to viscosity instead of any cooling mechanism. Chakrabarti & Das (2004); had shown that, with the increase of viscosity parameter, in the energy-angular momentum parameter space, the domain of shock decreases. We know viscosity transports angular momentum outwards, while the specific energy increases inwards.…”