Boson stars: alternatives to primordial black holes? Original Research Article

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 `universalʹ axion of effective string models, their total gravitational mass will be in the most likely range of ∼0.5M⊙ of MACHOs. According to this framework, gravitational microlensing is indirectly “weighing” the axion mass, resulting in ∼10−10 eV/c2. 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.