Boson Stars: Alternatives to primordial black holes?

TL;DR

This paper explores boson stars as potential dark matter candidates, discussing their formation, stability, and observational implications, especially in relation to primordial black holes and gravitational microlensing.

Contribution

It reviews the astrophysical relevance of boson stars, their formation, stability, and potential as dark matter, highlighting their possible role as MACHOs and their observational signatures.

Findings

Boson stars could account for a significant fraction of dark matter.

Gravitational microlensing can indirectly measure axion mass.

Boson stars with axion-like particles have masses around 0.5 M_.

Abstract

The present surge for the astrophysical relevance of boson stars stems from the speculative possibility that these compact objects could provide a considerable fraction of the non-baryonic part of dark matter within the halo of galaxies. For a very light `universal' axion of effective string models, their total gravitational mass will be in the most likely range of \sim 0.5 M_\odot of MACHOs. According to this framework, gravitational microlensing is indirectly ``weighing" the axion mass, resulting in \sim 10^{-10} eV/c^2. This conclusion is not changing much, if we use a dilaton type self-interaction for the bosons. Moreover, we review their formation, rotation and stability as likely candidates of astrophysical importance.