On geodesic dynamics in deformed black-hole fields

TL;DR

This paper investigates how the presence of matter like discs or rings around black holes affects the stability of particle orbits, revealing potential chaos in geodesic motion which impacts astrophysical observations.

Contribution

It demonstrates that additional matter distributions can induce chaotic geodesic behavior around black holes, challenging assumptions of stability in idealized models.

Findings

Geodesic motion can become chaotic due to matter perturbations.

The strength and nature of chaos depend on parameters of the matter distribution.

Implications for observational phenomena in galactic nuclei.

Abstract

"Almost all" seems to be known about isolated stationary black holes in asymptotically flat space-times and about the behaviour of {\em test} matter and fields in their backgrounds. The black holes likely present in galactic nuclei and in some X-ray binaries are commonly being represented by the Kerr metric, but actually they are not isolated (they are detected only thanks to a strong interaction with the surroundings), they are not stationary (black-hole sources are rather strongly variable) and they also probably do not live in an asymptotically flat universe. Such "perturbations" may query the classical black-hole theorems (how robust are the latter against them?) and certainly affect particles and fields around, which can have observational consequences. In the present contribution we examine how the geodesic structure of the static and axially symmetric black-hole space-time responds to the presence of an additional matter in the form of a thin disc or ring. We use several different methods to show that geodesic motion may become chaotic, to reveal the strength and type of this irregularity and its dependence on parameters. The relevance of such an analysis for galactic nuclei is briefly commented on.