Dynamics of hot accretion flow with thermal conduction

Abstract

The purpose of this paper is to explore the dynamical behaviour of hot accretion flows with thermal conduction. The importance of thermal conduction in hot accretion flows is confirmed by observations of the hot gas that surrounds Sgr A* and a few other nearby galactic nuclei. In this research, the effect of thermal conduction is studied through a saturated form, as is appropriate for weakly collisional systems. The angular momentum transport is assumed to be a result of viscous turbulence and the α‐prescription is used for the kinematic coefficient of viscosity. The equations of accretion flow are solved in a simplified one‐dimensional model that neglects the latitudinal dependence of the flow. To solve the integrated equations that govern the dynamical behaviour of the accretion flow, we have used an unsteady self‐similar solution. The solution provides some insights into the dynamics of quasi‐spherical accretion flow and avoids the limits of the steady self‐similar solution. In comparison with accretion flows without thermal conduction, the disc generally becomes cooler and denser. These properties are qualitatively consistent with simulations performed in hot accretion flows. Moreover, the angular velocity increases with the magnitude of conduction, while the radial infall velocity decreases. The mass accretion rate on to the central object is reduced in the presence of thermal conduction. We found that viscosity and thermal conduction have opposite effects on the physical variables. Furthermore, the flow represents a transonic point that displaces inward with the magnitude of conduction or viscosity.

Viscous and resistive accretion flows with radially self-similar outflows

“…Thus, the viscous torque increases with the temperature (). These properties are also consistent with the results of Faghei (2011).…”

“…The solutions in Figs 1 and 2 represent the radial inflow speed, c 1 , and the sound speed, c 3 , both of which increase with the magnitude of resistivity (). These properties are qualitatively consistent the results of Faghei (2011). The density profiles, c 0 , show that density decreases by adding resistivity.…”

“…Studies of resistive and magnetized ADAFs (e.g. Faghei 2011) imply that the solution for a set of the input parameters reaches a non‐rotating limit at a specific value of Π, which we call Π c . Assuming c 2 = 0 and s = l =ξ= 0 (no wind case) in equations ()–(), Π c can be written as For typical values of the adiabatic index and advection parameter in ADAFs, γ= 4/3 and f = 1, we can write Π c = 18 P m .…”

Self-similar solutions of viscous and resistive ADAFs with thermal conduction

“…As, with the magnitude of γ , the inflow and sound speed increase, while the rotational velocity decreases. This is in accord with dynamical study of hot accretion flow (Faghei 2011b). Moreover, Fig.…”

Role of thermal conduction in an advective accretion with bipolar outflows

“…Some authors investigated role of a saturated form of the thermal conduction in ADAFs using height-integrated equations (e.g., Abbassi et al 2008;Ghanbari et al 2009;Faghei 2012Faghei , 2013Faghei , 2012. Despite the positivity of Bernoulli parameter for these one-dimensional ADAF solutions and possible emergence of bipolar outflows, it is unlikely to study one-dimensional ADAFs with outflows self-consistently unless the outflows are included in a phenomenological way (e.g., Shadmehri 2008;Bu et al 2009).…”