Curved accretion disks around rotating black holes without reflection symmetry

TL;DR

This paper explores how reflection asymmetry in rotating black holes affects accretion disk structure and observational spin measurements, revealing that such asymmetry causes the disk to become curved and alters the innermost stable orbits.

Contribution

It introduces a model for Kerr-like black holes without reflection symmetry and analyzes how this asymmetry impacts accretion disk properties and spin measurement accuracy.

Findings

Accretion disks become curved surfaces rather than flat.

Reflection asymmetry shrinks the prograde innermost stable circular orbit.

Spin measurements assuming Kerr geometry may overestimate true spins.

Abstract

Rotating black holes without equatorial reflection symmetry can naturally arise in effective low-energy theories of fundamental quantum gravity, in particular, when parity-violating interactions are introduced. Adopting a theory-agnostic approach and considering a recently proposed Kerr-like black hole model, we investigate the structure and properties of accretion disk around a rotating black hole without reflection symmetry. In the absence of reflection symmetry, the accretion disk is in general a curved surface in shape, rather than a flat disk lying on the equatorial plane. Furthermore, the parameter $\epsilon$ that controls the reflection asymmetry would shrink the size of the prograde innermost stable circular orbits, and enhance the efficiency of the black hole in converting rest-mass energy to radiation during accretion. The retrograde innermost stable circular orbits are stretched but the effects are substantially suppressed. In addition, we find that spin measurements based on the gravitational redshift observations of the disk, assuming a Kerr geometry, may overestimate the true spin values if the central object is actually a Kerr-like black hole with conspicuous equatorial reflection asymmetry. The qualitative results that the accretion disk becomes curved and the prograde innermost stable circular orbits are shrunk turn out to be generic in our model when the reflection asymmetry is small.