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.
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