Gravitational redshifts in electromagnetic bursts occuring near Schwarzschild horizon

TL;DR

This paper demonstrates through numerical analysis that electromagnetic bursts near a Schwarzschild black hole's horizon can exhibit deviations from standard gravitational redshift predictions due to strong backscattering effects, including potential blueshifts.

Contribution

It provides the first numerical evidence that strong backscattering near a black hole horizon can invalidate the standard gravitational redshift formula for electromagnetic pulses.

Findings

Mean frequency does not obey standard redshift formula.

Backscatter-induced blueshift observed in outgoing radiation.

Redshift depends on the frequency of the electromagnetic pulse.

Abstract

It was suggested earlier that the gravitational redshift formula can be invalid when the effect of the backscattering is strong. It is demonstrated here numerically, for an exemplary electromagnetic pulse that is: i) initially located very close to the horizon of a Schwarzschild black hole and ii) strongly backscattered, that a mean frequency does not obey the standard redshift formula. Redshifts appear to depend on the frequency and there manifests a backscatter-induced blueshift in the outgoing radiation.