Low Angular Momentum Black Hole Accretion: First GRMHD Evidence of Standing Shocks

TL;DR

This paper presents the first GRMHD simulation evidence of stable standing shocks in low angular momentum black hole accretion flows, revealing new insights into plasma behavior and variability signatures near black holes.

Contribution

It demonstrates the formation and persistence of standing shocks in low-angular-momentum accretion flows using multi-dimensional GRMHD simulations, a novel finding in the field.

Findings

Stable standing shocks are observed in low angular momentum accretion flows.

Shock dynamics may explain observed variability like flares and QPOs.

Simulations confirm the standard and normal evolution (SANE) regime.

Abstract

Understanding the dynamics of low angular momentum accretion flow around black holes (BHs) is essential for probing extreme plasma behavior in strong gravity, where shock formation can naturally produce variability signatures. In this paper, we perform general relativistic magnetohydrodynamic (GRMHD) simulations of low angular momentum accretion flows onto a BH with different BH spins to investigate the accretion dynamics near the central BH region. The simulation results show the standard and normal evolution (SANE) regime in all cases. In particular, we report the formation and persistence of standing shocks in low-angular-momentum accretion flows using multi (two and three)-dimensional GRMHD simulations for the first time. Previous studies did not detect such stable standing shock structures, making our findings a significant advancement in this field. The finding of shock dynamics can be further associated with some radiation features, such as flares observed in Sgr~A$^\ast$ and quasi-periodic oscillation (QPO) signals detected in some XRBs and AGNs.