Revisited equilibrium solution of Fishbone and Moncrief torus for extended GRMHD simulations

TL;DR

This paper revisits the Fishbone and Moncrief torus solution, demonstrating its stability in non-Kerr spacetimes, which is crucial for testing gravity theories with horizon-scale black hole images.

Contribution

It generalizes the FM torus solution to non-Kerr spacetimes and confirms its stability through hydrodynamic simulations, aiding future GRMHD modeling.

Findings

FM torus is stable in non-Kerr spacetime.

The generalized solution can be used for extended Kerr black holes.

Supports testing gravity theories with horizon-scale images.

Abstract

Accretion physics has become more important recently due to the detection of the first horizon-scale images of the super-massive black holes of M\,87$^*$ and Sgr~A$^*$ by the Event Horizon Telescope (EHT). General relativistic magnetohydrodynamic (GRMHD) simulations of magnetized accretion flows onto a Kerr black hole have been used to interpret them. However, further testing the theory of gravity by using horizon-scale images requires performing consistent GRMHD simulations in non-Kerr spacetime. In this paper, we revisited the hydrodynamical equilibrium solution of the Fishbone and Moncrief (FM) torus that can be used to study any stationary, axisymmetric, vacuum, or non-vacuum spacetime. Further, we check the stability of the FM torus in non-Kerr spacetime by general relativistic hydrodynamic simulations. We find that FM torus in non-Kerr spacetime is indeed stable under long-term evolution. We conclude that the generalized FM torus solution would be very useful for creating new GRMHD libraries in extended Kerr black holes.