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 multispecies 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 luminosity, 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.
