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

TL;DR

This paper explores viscous, cooling, variable adiabatic index accretion flows onto black holes, deriving solutions with shocks and analyzing their luminosity and efficiency across different parameters.

Contribution

It introduces a generalized Bernoulli parameter for viscous, cooling flows with variable adiabatic index and provides comprehensive transonic solutions including shock conditions.

Findings

Shock solutions are more luminous than shock-free flows.

Luminosity can reach up to 1.2 times Eddington limit depending on parameters.

Steady shock solutions exist even at high viscosity and accretion rates.

Abstract

We investigated accretion on to black holes in presence of viscosity and cooling, by employing an equation of state with variable adiabatic index and multi-species fluid. We obtained the expression of generalized Bernoulli parameter which is a constant of motion for an accretion flow in presence of viscosity and cooling. We obtained all possible transonic solutions for a variety of boundary conditions, viscosity parameters and accretion rates. We identified the solutions with their positions in the parameter space of generalized Bernoulli parameter and the angular momentum on the horizon. We showed that a shocked solution is more luminous than a shock-free one. For particular energies and viscosity parameters, we obtained accretion disc luminosities in the range of $10^{-4}-1.2$ times Eddington limit, and the radiative efficiency seemed to increase with the mass accretion rate too. We found steady state shock solutions even for high-viscosity parameters, high accretion rates, and for wide range of composition of the flow, starting from purely electron-proton to lepton-dominated accretion flow. However, similar to earlier studies of inviscid flow, accretion shock was not obtained for electron-positron pair plasma.