Are black holes in alternative theories serious astrophysical candidates? The case for Einstein-Dilaton-Gauss-Bonnet black holes

TL;DR

This paper explores Einstein-Dilaton-Gauss-Bonnet black holes as viable astrophysical objects, analyzing their stability, rotation, and geodesic properties to identify potential observational differences from standard black holes.

Contribution

It extends previous work by establishing stability against axial perturbations and analyzing rotating solutions, highlighting observable differences from General Relativity black holes.

Findings

Dilatonic black holes are stable against radial and axial perturbations.

Rotating solutions show measurable differences in ISCO and orbital frequencies.

Differences could help distinguish these black holes in future astrophysical observations.

Abstract

It is generally accepted that Einstein's theory will get some as yet unknown corrections, possibly large in the strong field regime. An ideal place to look for these modifications is around the vicinities of compact objects such as black holes. Our case study here are Dilatonic Black Holes, which arise in the framework of Gauss-Bonnet couplings and one-loop corrected four-dimensional effective theory of heterotic superstrings at low energies. These are interesting objects as a prototype for alternative, yet well-behaved gravity theories: they evade the "no-hair" theorem of General Relativity but were proved to be stable against radial perturbations. We investigate the viability of these black holes as astrophysical objects and try to provide some means to distinguish them from black holes in General Relativity. We start by extending previous works and establishing the stability of these black holes against axial perturbations. We then look for solutions of the field equations describing slowly rotating black holes and study geodesic motion around this geometry. Depending on the values of mass, dilaton charge and angular momentum of the solution, one can have measurable differences in the ISCO location and orbital frequency, relatively to black holes in General Relativity. Such differences may be useful in future experiments, to discriminate between alternative theories of gravity.