Coherent forward scattering of starlight by a cloud of atomic hydrogen

TL;DR

This paper discusses how coherent forward scattering by interstellar atomic hydrogen clouds can significantly enhance the observed brightness of starlight, based on the coherence and size of Fresnel zones.

Contribution

It introduces a theoretical framework for understanding how large-scale coherence effects lead to enhanced forward scattering in interstellar hydrogen clouds.

Findings

Enhanced irradiance due to coherence effects

Relevance of large Fresnel zones (~1500 km) in astrophysical scattering

Potential implications for astronomical observations of interstellar clouds

Abstract

Theory predicts that a plane wave scattered by a thin slab of gas yields, in the forward direction and under specific circumstances, a larger irradiance than would be observed in the absence of the gas. This enhanced Rayleigh scattering depends on the size of the Fresnel zones at the slab location, as seen from the observer's position, and results from the coherence of the scattering. On astronomical scales the exceptional size of Fresnel zones (~1500km) has particular relevance when considering forward-scattered starlight by an interstellar cloud of atomic hydrogen.