GRMHD beyond Kerr: An extension of the HARM code for thin disks to non-Kerr spacetimes

TL;DR

This paper extends the HARM code to simulate thin accretion disks around non-Kerr black holes, enabling tests of general relativity with more general spacetime geometries.

Contribution

It introduces a parametrically deformed black hole metric into the HARM code, allowing for simulations of accretion disks in non-Kerr spacetimes.

Findings

Disk structure and stability analyzed in non-Kerr spacetimes

Radiative efficiency of disks studied with the extended model

Fe Kα profiles computed for simplified scenarios

Abstract

Black hole based tests of general relativity have proliferated in recent times with new and improved detectors and telescopes. Modelling of the black hole neighborhood, where most of the radiation carrying strong-field signature originates, is of utmost importance for robust and accurate constraints on possible violations of general relativity. As a first step, this paper presents the extension of general relativistic magnetohydrodynamic simulations of thin accretion disks to parametrically deformed black holes that generalize the Kerr solution. The extension is based on \textsc{harmpi}, a publicly available member of the \textsc{harm} family of codes, and uses a phenomenological metric to study parametric deviations away from Kerr. The extended model is used to study the disk structure, stability, and radiative efficiency. We also compute the Fe K$\alpha$ profiles in simplified scenarios and present an outlook for the future.