Dissimilar Donuts in the Sky? Effects of a Pressure Singularity on the Circular Photon Orbits and Shadow of a Cosmological Black Hole

TL;DR

This paper explores how a pressure cosmological singularity could influence black hole shadows at cosmological redshifts, potentially explaining variations in observed shadows and addressing the H0-tension problem.

Contribution

It demonstrates that pressure singularities can affect photon orbits and black hole shadows, providing a novel link between cosmological events and observable black hole features.

Findings

Pressure singularity impacts circular photon orbits around cosmological black holes.

Absence of photon orbits before the singularity could alter black hole shadows.

Future observations of black hole shadows at specific redshifts might reveal signatures of pressure singularities.

Abstract

The black hole observations obtained so far indicate one thing: similar "donuts" exist in the sky. But what if some of the observed black hole shadows that will obtained in the future are different from the others? In this work the aim is to show that a difference in the shadow of some observed black holes in the future, might explain the $H_0$-tension problem. In this letter we investigate the possible effects of a pressure cosmological singularity on the circular photon orbits and the shadow of galactic supermassive black holes at cosmological redshifts. Since the pressure singularity is a global event in the Universe, the effects of the pressure singularity will be imposed on supermassive black holes at a specific redshift. As we show, the pressure singularity affects the circular photon orbits around cosmological black holes described by the McVittie metric, and specifically, for some time before the time instance that the singularity occurs, the photon orbits do not exist. We discuss the possible effects of the absence of circular photon orbits on the shadow of these black holes. Our idea indicates that if a pressure singularity occurred in the near past, then this could have a direct imprint on the shadow of supermassive galactic black holes at the redshift corresponding to the time instance that the singularity occurred in the past. Thus, if a sample of shadows is observed in the future for redshifts $z\leq 0.01$, and for a specific redshift differences are found in the shadows, this could be an indication that a pressure singularity occurred, and this global event might resolve the $H_0$-tension as discussed in previous work. However, the observation of several shadows at redshifts $z\leq 0.01$ is rather a far future task.