Dissimilar donuts in the sky? Effects of a pressure singularity on the circular photon orbits and shadow of a cosmological black hole

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 H0-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 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 H0-tension as discussed in previous work. However, the observation of several shadows at redshifts z 0.01 is rather a far future task.

A Reanalysis of the Latest SH0ES Data for H0: Effects of New Degrees of Freedom on the Hubble Tension

“…A fourth approach related to the previous one is based on a possible change of the physical laws (e.g., a gravitational transition [142,143]) during the past 200 Myrs (z 0.01) when the light of the Cepheid calibrator hosts was emitted [143][144][145][146][147][148][149][150][151][152]. In this context, new degrees of freedom should be allowed for the modeling of either Cepheid calibrators and/or SnIa to allow for the possibility of this physics change.…”

The Unsettled Number: Hubble’s Tension

“…Other possible effects may come from alternative models to ΛCDM in which pressure singularities may exist, which change the shadows of black holes and, therefore H 0 . This could eventually resolve the Hubble tension [230,231].…”

Black hole shadow and chaos bound violation in f(T) teleparallel gravity

“…1 See Refs. [25][26][27][28][29][30][31][32][33] for several recent works on BH shadow and QNMs beyond GR.…”