Viscous Accreting Magnetofluids around a Static Compact Object in Final Stages of Accretion Flow

Abstract

The dynamics of the stationary axisymmetric configuration of accreting magnetofluids surrounding a nonrotating compact object in the final stages of accretion flow is presented here. We discuss two classes of solutions for the angular momentum: a Keplerian solution, which demands no accretion flow for the fluids, and a non-Keplerian solution, which requires a radial inflow velocity for the matter. For the special case of no presence of electromagnetic fields, two sets of self-consistent analytical solutions of fully relativistic fluid equations are obtained separately for two different equations of state. The effect of the bulk viscosity coefficient on the physical functions was investigated for each state, as well as the bounds that exert on the free parameters due to last stages of the accretion-flow condition. To resolve the magnetohydrodynamical equations, we were inspired by previous sets of solutions, since the magnetofluid equations are just the same as the fluid ones in the case of vanishing electromagnetic fields. The azimuthal current in magnetofluids doesn't modify the dipolar configuration of the central object magnetic field, owing to the lack of a finite resistivity. The presence of this magnetic field doesn't affect the azimuthal velocity of the plasma, but does slow down its radial inflow, and decrease the density and pressure of the plasma. Despite the role importance of the bulk viscosity on the fluids' dynamics in the absence of electromagnetic fields, exerting the magnetic field decreases this role.

Accreting magnetofluids around a rotating compact object with a dipolar magnetic field

“…In other words, in this case, there is no angular momentum transport mechanism. Thus, these solutions are indicated the accretion flow in the final stages once most of the gas orbital angular momentum already has been removed in the sense that in those instants the fluids almost pass directly into the central compact object (Ghanbari & Shaghaghian 2009). Close to the black hole event horizon, the gas temperature and velocities become extremely high (Popham & Gammie 1998) and gradually fall off outwards.…”

“…This points to the fact that the density term in the pressure relation () dominates and the presence of bulk viscosity fades. Indeed, it is an admissible result that the importance of bulk viscosity vanishes while the electromagnetic field appears in the system (Bhaskaran & Prasanna 1990; Ghanbari & Shaghaghian 2009). The conductivity consideration gives rise to the presence of the magnetic field in the governing equations () and ().…”