Dynamical Lensing Tomography of Black Hole Ringdown

TL;DR

This paper explores how strong gravitational lensing near black holes affects photon trajectories during black hole mergers, revealing patterns that could improve imaging of such extreme events.

Contribution

It introduces a novel analysis of photon deflection angles in black hole environments, linking lensing patterns to gravitational wave signals during ringdown.

Findings

Deflection angle mimics gravitational wave ringdown patterns.

Late-time deflection exhibits inverse cubic dependence on time.

Photon approach to the photon ring shows exponential increase in deviation.

Abstract

Strong gravitational lensing occurs when photons pass through the vicinity of a black hole. We investigate this phenomenon in the context of a gravitational-wave event, specifically when a black hole is settling into its final state. The deflection angle of photons mimics the ringdown pattern of the gravitational wave at intermediate times. At late times it has an inverse cubic dependence on observation time. The deviation angle increases exponentially as photons approach the photon ring orbit, reflecting its unstable nature. Our findings are directly applicable to imaging scenarios involving stars against the background of compact binaries, or circumbinary accretion disks, particularly during the merger of two black holes.