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

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 ∼ 10%. 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.

Shadows of Kerr-Vaidya-like black holes

“…s E 2 , and we have switched to a different notation for the celestial coordinates Φ, Θ for clarity having derived their eventual expressions. In particular, we note that θ inc measures the angle between the black hole's spin axis as defined by θ = 0(the zero locus of g φφ ) and the observer, with e 3 being parallel to the line of sight connecting the observer to the origin of the Boyer-Lindquist-like chart in (9).…”

“…The boundary curve of the black hole shadow emerges from light rays that spiral asymptotically from the photon region demarcating the boderline between light rays that will eventually be captured by the black hole and those that escape to infinity [3]. i The geometry of this boundary curve depends on the background metric which could thus be probed by EHT observations [7,8,9,10,11,12] . For example, the shadow geometry of Sgr * has been used to exclude the central object being a Reissner-Nordstrom-type naked singularity or a traversable Misner-Thorne wormhole [8].…”