Possible observational windows for quantum effects from black holes

TL;DR

This paper explores how quantum effects near black hole horizons could produce observable phenomena, like distortions in the black hole shadow, by analyzing couplings that transfer information while maintaining near-horizon geometry.

Contribution

It introduces a parameterization of quantum couplings affecting black hole horizons, proposing observable effects that could test quantum gravity models.

Findings

Quantum couplings can cause detectable deflections of near-horizon geodesics.

Such effects may distort black hole images like the shadow and photon ring.

Potential observational signatures include disruptions in accretion flows and gravitational wave signals.

Abstract

Quantum information transfer necessary to reconcile black hole evaporation with quantum mechanics, while approximately preserving regular near-horizon geometry, can be simply parameterized in terms of couplings of the black hole internal state to quantum fields of the black hole atmosphere. The necessity of transferring sufficient information for unitarization sets the strengths of these couplings. Such couplings via the stress tensor offer apparently significant advantages, and behave like quantum fluctuations of the effective metric near the horizon. At the requisite strength, these fluctuations, while soft (low energy/momentum), have significant magnitude, and so can deflect near-horizon geodesics that span distances of order the black hole radius. Thus, the presence of such couplings can result in effects that could be detected or constrained by observation: disruption of near-horizon accretion flows, scintillation of light passing close to the black hole, and alteration of gravitational wave emission from inspirals. These effects could in particular distort features of Sgr A* expected to be observed, e.g., by the Event Horizon Telescope, such as the black hole shadow and photon ring.