Study of general relativistic magnetohydrodynamic accretion flow around black holes

We present a novel approach to study the global structure of steady, axisymmetric, advective, magnetohydrodynamic (MHD) accretion flow around black holes in full general relativity (GR). Considering ideal MHD conditions and relativistic equation of state (REoS), we solve the governing equations to obtain all possible smooth global accretion solutions. We examine the dynamical and thermodynamical properties of accreting matter in terms of the flow parameters, namely energy (epsilon), angular momentum (L), and local magnetic fields. For a vertically integrated GRMHD flow, we observe that toroidal component (b(phi)) of the magnetic fields generally dominates over radial component (b(r)) at the disc equatorial plane. This evidently suggests that toroidal magnetic field indeed plays important role in regulating the disc dynamics. We further notice that the disc remains mostly gas pressure (p(gas)) dominated (beta= p(gas)/p(mag) > 1, p mag refers magnetic pressure) except at the near horizon region, where magnetic fields become indispensable (beta similar to 1). We observe that Maxwell stress is developed that eventually yields angular momentum transport inside the disc. Towards this, we calculate the viscosity parameter (alpha) that appears to be radially varying. In addition, we examine the underlying scaling relation between alpha and beta, which clearly distinguishes two domains coexisted along the radial extent of the disc. Finally, we discuss the utility of the present formalism in the realm of GRMHD simulation studies.

Automated summary

We present a novel approach to study the global structure of steady, axisymmetric, advective, magnetohydrodynamic (MHD) accretion flow around black holes in full general relativity (GR). Considering ideal MHD conditions and relativistic equation of state (REoS), we solve the governing equations to obtain all possible smooth global accretion solutions. We examine the dynamical and thermodynamical properties of accreting matter in terms of the flow parameters, namely energy (epsilon), angular momentum (L), and local magnetic fields. We observe that toroidal component of the magnetic fields generally dominates over radial component at the disc equatorial plane, suggesting the importance of toroidal magnetic field in regulating the disc dynamics. The disc remains mostly gas pressure dominated except at the near horizon region where magnetic fields become indispensable. We calculate the viscosity parameter and examine the scaling relation between alpha and beta, distinguishing two domains along the radial extent of the disc. We discuss the utility of the present formalism in GRMHD simulation studies.