Equatorially Asymmetric Magnetic Fields and Their Impact on Black Hole Accretion Dynamics

TL;DR

This study uses axisymmetric GRMHD simulations to show how equatorial magnetic field asymmetry affects black hole accretion flow structures, outflows, and variability, especially at low plasma beta values.

Contribution

It introduces the impact of equatorially asymmetric magnetic fields on accretion dynamics, a novel aspect not extensively explored in prior symmetric field studies.

Findings

Asymmetric magnetic fields cause inner disk structural changes.

They induce asymmetric outflows and inflow patterns.

Effects are stronger at lower plasma beta values.

Abstract

We investigate the impact of equatorial asymmetry in the magnetic field geometry on accretion dynamics around a spinning black hole using axisymmetric general relativistic magnetohydrodynamic simulations. We consider a Fishbone--Moncrief torus orbiting a Kerr black hole with spin parameter $a = 0.9375$, threaded by large-scale magnetic fields that are asymmetric about the equatorial plane. The degree of equatorial asymmetry in the magnetic field is parametrized by an angle, with values of $30^\circ$, $45^\circ$, and $60^\circ$. We examine how this equatorially asymmetric initial magnetic field configuration influences the magnetic field structure, accretion flow morphology, and angular momentum transport across a range of initial plasma beta values ($\beta = 0.007, 0.005, 0.001$). We find that such deformation in the magnetic field leads to noticeable changes in the inner disk structure, asymmetric outflow patterns in the poloidal plane, and time-dependent variations in accretion rates. These effects are generally more pronounced at lower beta values, where magnetic pressure dominates; in particular, the $30^\circ$ case at $\beta = 0.001$ exhibits strong and persistent asymmetric inflows and outflows. Our results demonstrate that equatorially asymmetric magnetic field configurations can significantly influence the structure and variability of relativistic accretion flows. These findings motivate future extensions to full three-dimensional studies, where black hole magnetosphere can be explored in a more general setting.