Dissipative advective accretion disc solutions with variable adiabatic index around black holes

Abstract

We investigated accretion on to black holes in presence of viscosity and\ncooling, by employing an equation of state with variable adiabatic index and\nmulti-species fluid. We obtained the expression of generalized Bernoulli\nparameter which is a constant of motion for an accretion flow in presence of\nviscosity and cooling. We obtained all possible transonic solutions for a\nvariety of boundary conditions, viscosity parameters and accretion rates. We\nidentified the solutions with their positions in the parameter space of\ngeneralized Bernoulli parameter and the angular momentum on the horizon. We\nshowed that a shocked solution is more luminous than a shock-free one. For\nparticular energies and viscosity parameters, we obtained accretion disc\nluminosities in the range of $10^{-4}-1.2$ times Eddington limit, and the\nradiative efficiency seemed to increase with the mass accretion rate too. We\nfound steady state shock solutions even for high-viscosity parameters, high\naccretion rates, and for wide range of composition of the flow, starting from\npurely electron-proton to lepton-dominated accretion flow. However, similar to\nearlier studies of inviscid flow, accretion shock was not obtained for\nelectron-positron pair plasma.\n