The Fate of Transonic Shocks around Black Holes and their Future Astrophysical Implications

TL;DR

This study uses advanced simulations to explore the formation and behavior of shocks in accretion flows onto black holes, revealing their dependence on magnetic fields, black hole spin, and flow parameters, with implications for jet formation.

Contribution

The paper presents the first detailed general relativistic simulations showing shock formation in low-angular-momentum accretion flows onto Kerr black holes, including effects of magnetic fields and black hole spin.

Findings

Shocks form naturally between sonic points in specific energy and angular momentum conditions.

Weak magnetic fields preserve shock structures, while strong fields suppress shocks and promote jets.

Higher black hole spins lead to faster jets and influence shock and outflow properties.

Abstract

Theoretical models have long predicted the existence of shocks in multi-transonic accretion flows onto a black hole, yet their fate under realistic general relativistic simulations has not been fully tested. In this study, we present results from high-resolution two-dimensional general relativistic hydrodynamic (GRHD) and general relativistic magnetohydrodynamic (GRMHD) simulations of low-angular-momentum accretion flows onto Kerr black holes, focusing on the formation of shocks in transonic accretion flow. We demonstrate that for specific combinations of energy and angular momentum, global shock solutions naturally emerge between multiple sonic points. These shocks are sustained in both corotating and counter-rotating cases, and their locations depend on specific energy, angular momentum, and the spin of the black hole which is in good agreement with analytical solutions. In magnetized flows, weak magnetic fields preserve the shock structure, whereas strong fields suppress it, enhancing turbulence and driving powerful, magnetically dominated jets/outflows. The strength and structure of the outflow also depend on a black hole spin and magnetization, with higher black hole spin parameters leading to faster jets. Shock solutions are found only in super-Alfv\'{e}nic regions, where kinetic forces dominate. Our findings provide important insights into the physics of hot corona formation and jet launching in low-angular-momentum accretion systems such as Sgr~A$^*$ (weak jet/outflow) and X-ray binaries.