Boson stars

A boson star (BS) is a compact, globally regular, configuration of self–gravitating boson fields with self–interaction, possessing a large particle number and mass. For reviews see. The boson fields can be motivated e. g. by supersymmetric Standard Models or by axion condensates. Interesting features of BSs are, e.g., that their angular momentum is quantized in terms of their scalar charge and that they can be almost as compact as BHs though without an event horizon. In the weak field region BSs are indistinguishable from BHs. BSs have been considered as alternatives for the galactic BHs, as models for the galactic halo, or part of dark matter within the galactic halos. Observational consequences have been investigated for rotation curves, gravitational redshift, accretion discs, and gravitational waves. In brane–world scenarios, where the extra dimension is effectively compactified by a warp factor, matter fields are typically confined on the brane whereas gravity extends into the extra dimension (bulk). The possibility to describe astrophysical objects within these models is an essential criterion for their viability. Thus, BS promise to be an ideal test–bed for such models.