Circular geodesics and thick tori around rotating boson stars

TL;DR

This paper investigates the properties of circular geodesics and thick accretion tori around rotating boson stars, highlighting differences from black holes that could be observed with future interferometers to identify the nature of compact objects.

Contribution

It provides a detailed analysis of stable circular orbits and accretion tori around boson stars, revealing unique features that distinguish them from black holes.

Findings

All circular orbits around boson stars are bound.

Cusp formation in accretion tori occurs only for strongly gravitating boson stars.

Allowed angular momentum ranges depend on boson star properties.

Abstract

Accretion disks play an important role in the evolution of their relativistic inner compact objects. The emergence of a new generation of interferometers will allow to resolve these accretion disks and provide more information about the properties of the central gravitating object. Due to this instrumental leap forward it is crucial to investigate the accretion disk physics near various types of inner compact objects now to deduce later constraints on the central objects from observations. A possible candidate for the inner object is the boson star. Here, we will try to analyze the differences between accretion structures surrounding boson stars and black holes. We aim at analysing the physics of circular geodesics around boson stars and study simple thick accretion tori (so-called Polish doughnuts) in the vicinity of these stars. We realize a detailed study of the properties of circular geodesics around boson stars. We then perform a parameter study of thick tori with constant angular momentum surrounding boson stars. This is done using the boson star models computed by a code constructed with the spectral solver library KADATH. We demonstrate that all the circular stable orbits are bound. In the case of a constant angular momentum torus, a cusp in the torus surface exists only for boson stars with a strong gravitational scalar field. Moreover, for each inner radius of the disk, the allowed specific angular momentum values lie within a constrained range which depends on the boson star considered. We show that the accretion tori around boson stars have different characteristics than in the vicinity of a black hole. With future instruments it could be possible to use these differences to constrain the nature of compact objects.