Photon escape from the ISCO of a rotating black hole in Asymptotic Safety

TL;DR

This paper investigates photon escape probabilities and blueshifts from the ISCO of rotating black holes in asymptotic safety, revealing quantum gravity effects can increase photon observability despite a reduced ISCO radius.

Contribution

It provides the first analysis showing quantum gravity effects can enhance photon escape probability and blueshift from the ISCO of rotating black holes in asymptotic safety.

Findings

Quantum gravity effects increase PEP and MOB near critical values of the quantum parameter.

Contrary to expectations, the ISCO radius reduction does not decrease photon escape metrics.

Results suggest quantum effects dominate over classical predictions at the ISCO level.

Abstract

We study isotropic emission of photons from the innermost stable circular orbit (ISCO) of a subextremal rotating black hole (BH) in asymptotic safety (AS). We calculate both the photon escape probability (PEP) and the maximum observable blueshift (MOB) of photons to reach infinity, and compare with the corresponding results for photon emission from the ISCO of a classical Kerr BH. In AS, quantum gravity effects reduce the radius of the ISCO, therefore quantum gravity effects should reduce the PEP and MOB of photons from emitters moving on the ISCO. We show that this is not the case and that, when rotating BHs with high spin are considered and the quantum parameter (which encodes the quantum gravity effects) increases towards its critical value, which is different for different spin values, the PEP and MOB also increase despite the reduction of the ISCO radius. Our results on the PEP show explicitly how quantum gravity effects start to dominate over the classical background at the level of the ISCO. We also briefly discuss the relation between these quantum gravity modifications and particular features of the shadow of a rotating BH in AS.