| Abstract : | Magnetic fields play a crucial role in driving the accretion flows around black holes (BHs). However, the underlying mechanisms that govern accretion flow are not well understood. In this study, we investigate advective transonic accretion flows (ADAF) around a BH and analyze the flow dynamics in the presence of radial and toroidal magnetic fields. We consider the disk to be thin, and axisymmetric in the equatorial plane (θ ∼ π/2). Here, we present the first-ever analytical study of the steady-state general-relativistic magneto-hydrodynamics (GRMHD) accretion flows around BHs to the best of our knowledge. We connect the flow properties with the global constant of motion of the accreting fluid, namely the energy (E), angular momentum (L), and the local magnetic fields, respectively. We use the GRMHD flow equations to find critical points and obtain the global transonic accretion solutions. The thermodynamical counterpart is taken care of by the relativistic equation of state (REoS). We find that even a weakly magnetized flow (β >> 1) can transport angular momentum outwards. Additionally, we define a model viscosity parameter (αtot) that develops within the disk due to the magnetic stress and find it to be radially varying in a ‘U’ shape, which was not reported earlier. Interestingly, our 1.5D analytical study confirms that magnetic fields are dynamically important (several thousand Gauss for a 10M_{\rm sun} BH, (β ∼ 1)) in the near horizon region, which is in favor of the recent observations by the Event Horizon Telescope (EHT). |
