The Distribution and Annihilation of Dark Matter Around Black Holes

TL;DR

This paper models dark matter distribution around Kerr black holes using Monte Carlo simulations, revealing how black hole spin and dark matter properties influence annihilation signals and gamma-ray spectra.

Contribution

It introduces a Monte Carlo approach to calculate dark matter particle orbits and resulting annihilation signals near spinning black holes, extending previous analytic work.

Findings

High annihilation efficiencies (>600%) for rapidly spinning black holes.

Gamma-ray spectra features depend on black hole spin and dark matter properties.

Significant observable flux from dark matter annihilation near black hole horizons.

Abstract

We use a Monte Carlo code to calculate the geodesic orbits of test particles around Kerr black holes, generating a distribution function of both bound and unbound populations of dark matter particles. From this distribution function, we calculate annihilation rates and observable gamma-ray spectra for a few simple dark matter models. The features of these spectra are sensitive to the black hole spin, observer inclination, and detailed properties of the dark matter annihilation cross section and density profile. Confirming earlier analytic work, we find that for rapidly spinning black holes, the collisional Penrose process can reach efficiencies exceeding $600\%$, leading to a high-energy tail in the annihilation spectrum. The high particle density and large proper volume of the region immediately surrounding the horizon ensures that the observed flux from these extreme events is non-negligible.