Quantum gravity lights up spinning black holes

TL;DR

This paper proposes that quantum gravity effects can cause a black hole to transition into a horizonless spacetime with observable lensing features, especially in highly spinning black holes, potentially detectable by next-generation telescopes.

Contribution

It introduces a mechanism where near-critical spin amplifies quantum gravity effects, leading to observable changes in black hole imaging and lensing features.

Findings

Additional internal photon rings appear due to quantum effects.

Internal and external photon rings merge into crescent shapes with increasing spin.

Next-generation Event Horizon Telescope could detect these quantum-induced features.

Abstract

Quantum-gravity effects in black holes are generally expected to be unobservable if they set in at transplanckian curvature scales. Here, we challenge this expectation. A near-critical spin parameter can serve as a lever arm that translates Planckian quantum-gravity effects to a global change in the spacetime: the horizon dissolves and the black hole "lights up". We investigate this transition between a black hole and a horizonless spacetime and find that additional lensing features appear instantaneously, when the quantum-gravity effect is added. In the presence of an accretion disk, a second set of internal photon rings appears in addition to the exponentially stacked set of external photon rings. The internal and external photon rings merge into cresent-like features as a function of increasing spin parameter. We explore how these simulated images would be reconstructed by a radio-very-long-baseline-interferometry array like the Event Horizon Telescope. We find that a future next-generation Event Horizon Telescope may be sensitive to the additional lensing features.