Spherical scalar waves and gravity - red shift and backscattering

TL;DR

This paper analyzes how scalar waves interact with strong gravitational fields, focusing on redshift and backscattering effects outside horizons, and provides bounds on their influence, with potential astrophysical implications.

Contribution

It offers a rigorous quantitative analysis of backscattering effects on scalar waves near strong gravitational fields, highlighting conditions where backscattering is negligible.

Findings

Backscattering reduces outgoing radiation flux near apparent horizons.

Backscattering is negligible when emitter is far from black hole (2m_0 / R << 1).

Results have potential astrophysical consequences for wave propagation near black holes.

Abstract

This article investigates the interaction of a spherically symmetric massless scalar field with a strong gravitational field. It focuses on the propagation of waves in regions outside any horizons. The two factors acting on the waves can be identified as a redshift and a backscattering. The influence of backscattering on the intensity of the outgoing radiation is studied and rigorous quantitative upper bounds obtained. These show that the total flux may be decreased if the sources are placed in a region adjoining an apparent horizon. Backscattering can be neglected in the case $2m_0 /R<< 1$, that is when the emitter is located at a distance from a black hole much larger than the Schwarzschild radius. This backscattering may have noticeable astrophysical consequences.