The Black Hole: Scatterer, Absorber and Emitter of Particles

TL;DR

This paper presents a novel computational approach to analyze black hole wave scattering, revealing a unique oscillatory absorption spectrum caused by diffraction effects, which distinguishes black holes from ordinary absorptive bodies.

Contribution

The author develops exact methods to compute black hole absorption spectra, uncovering diffraction patterns and generalizing the optical theorem for black holes, highlighting features overlooked in previous studies.

Findings

Black hole absorption spectrum exhibits oscillatory diffraction patterns.

Absorption occurs only at the singularity (origin).

Features are universal across higher-dimensional black holes.

Abstract

Accurate and powerful computational methods developed by the author for the wave scattering by black holes allow to obtain the highly non trivial total absorption spectrum of the Black Hole. As well as partial wave phase shifts and cross sections (elastic and inelastic), the angular distribution of absorbed and scattered waves, and the Hawking emission rates. The exact total absorption spectrum of waves by the Black Hole has as a function of frequency a remarkable oscillatory behaviour characteristic of a diffraction pattern. This is an unique distinctive feature of the black hole absorption, and due to its r = 0 singularity. Ordinary absorptive bodies and optical models do not present these features. The unitarity optical theorem is generalized to the Black Hole case explicitly showing that absorption ocurrs only at the origin. All these results allow to understand and reproduce the Black Hole absorption spectrum in terms of Fresnel-Kirchoff diffraction theory: by the interference of the absorbed rays arriving at the origin through different optical paths. These fundamental features of the Black Hole Absorption will be present for generic higher dimensional Black Hole backgrounds, and whatever the low energy effective theory they arise from. In recent and increasing litterature devoted to compute absorption cross sections (grey body factors) of black holes (whatever ordinary, stringy, D-braned), the fundamental remarkable features of the Black Hole Absorption spectrum are overlooked.