On-Axis scalar absorption cross section of Kerr-Newman black holes: Geodesic analysis, sinc and low-frequency approximations

TL;DR

This paper analyzes how scalar waves are absorbed by Kerr-Newman black holes using geodesic methods, providing accurate approximations that match numerical results, enhancing understanding of black hole absorption properties.

Contribution

It introduces sinc and low-frequency approximations for the scalar absorption cross section of Kerr-Newman black holes based on geodesic analysis, validated against numerical data.

Findings

Sinc and low-frequency approximations agree well with numerical results.

Absorption cross section can be described using photon orbit parameters.

Geodesic analysis effectively models scalar wave absorption.

Abstract

We investigate null geodesics impinging parallel to the rotation axis of a Kerr-Newman black hole, and show that the absorption cross section for a massless scalar field in the eikonal limit can be described in terms of the photon orbit parameters. We compare our sinc and low-frequency approximations with numerical results, showing that they are in excellent agreement.