Photon Ring Astrometry for Superradiant Clouds

TL;DR

This paper explores how superradiant clouds around black holes can cause detectable photon deflections, proposing a method to observe these effects with the Event Horizon Telescope to probe ultralight bosons.

Contribution

It introduces a novel approach to detect superradiant clouds via photon ring autocorrelations, expanding the search for ultralight bosons beyond previous methods.

Findings

Photon geodesic deviations can be amplified near critical bound orbits.

Photon ring autocorrelations can detect superradiant clouds.

Proposed method probes new parameter space for ultralight bosons.

Abstract

Gravitational atoms produced from the superradiant extraction of rotational energy of spinning black holes can reach energy densities significantly higher than that of dark matter, turning black holes into powerful potential detectors for ultralight bosons. These structures are formed by coherently oscillating bosons, which induce oscillating metric perturbations deflecting photon geodesics passing through their interior. The deviation of nearby geodesics can be further amplified near critical bound photon orbits. We discuss the prospect of detecting this deflection using photon ring autocorrelations with the Event Horizon Telescope and its next-generation upgrade, which can probe a large unexplored region of the cloud mass parameter space when compared with previous constraints.