Geometrical-optics analysis of the interaction between light and gravitational waves from binaries

TL;DR

This paper analyzes how light interacts with gravitational waves from binaries using geometrical optics, focusing on the gravitational Faraday rotation effect, with potential observable implications for astrophysical sources.

Contribution

It introduces a geometrical-optics framework to study light-gravitational wave interactions near binary sources, emphasizing the gravitational Faraday rotation effect.

Findings

Interaction effects accumulate over long light paths.

The gravitational Faraday rotation can be significant near the source.

Modeling with spherical gravitational waves captures the interaction dynamics.

Abstract

We consider a situation in which light emitted from the neighborhood of a binary interacts with gravitational waves from the binary (e.g., a supermassive black hole binary in a quasar, a binary pulsar, etc.). The effect is cumulative over the long path lengths of light propagation and might be appreciable if the interaction initially takes place close to the source of gravitational waves, where the strain amplitude can be large. This situation can be modeled effectively using spherical gravitational waves (i.e., transverse-traceless radially propagating waves), with the strain amplitude varying with the distance from the source to a field point where the two wavefronts of light and gravitational waves meet each other. Our analysis employs geometrical-optics methods in curved spacetime, where the curvature is due to gravitational waves propagating in a flat spacetime background. We place a particular focus on the effect of gravitational Faraday rotation (or Skrotskii/Rytov effect) resulting from the interaction between light and gravitational waves from binaries.