Testing black hole equatorial reflection symmetry using Sgr A* shadow images

TL;DR

This study uses Sgr A* black hole images to test for deviations from equatorial reflection symmetry predicted by general relativity, constraining possible new physics through the size of the black hole's shadow.

Contribution

It introduces a model-independent framework to constrain reflection symmetry violations in black hole spacetimes using observational shadow data.

Findings

Critical curve size is sensitive to reflection symmetry violations.

First constraints on reflection symmetry violation parameters using Sgr A* images.

Shadow size consistent with GR within approximately 10%.

Abstract

The recently released images of the supermassive black holes in the M87 galaxy and the galaxy of our own make probing black hole spacetimes and testing general relativity (GR) possible. The violation of equatorial reflection symmetry of black hole spacetimes is clearly a smoking gun of physics beyond GR. In this paper, we place constraints on the violation of black hole reflection symmetry using the bounds on the ring size of the Sgr A* black hole images, which are consistent with the critical curve radius predicted in GR within $\sim10\%$. Adopting a theory-agnostic framework, we consider a Kerr-like metric in which the violation of reflection symmetry is parametrized by a single parameter, without altering the multipoles of the black hole. The critical curves are always vertically symmetric due to the existence of hidden symmetry associated with the Killing tensor, even though the spacetime is reflection asymmetric. We find that the size of critical curves is sensitive to the amount of reflection symmetry being violated, and place the first constraints on the parameter space of the model using the Sgr A* images.