Relativistic axions from collapsing Bose stars
  The substructures of light bosonic (axion-like) dark matter may condense into
compact Bose stars. We study collapses of the critical-mass stars caused by
attractive self-interaction of the axion-like particles and find that these
processes proceed in an unexpected universal way. First, nonlinear self-similar
evolution (called "wave collapse" in condensed matter physics) forces the
particles to fall into the star center. Second, interactions in the dense
center create an outgoing stream of mildly relativistic particles which carries
away an essential part of the star mass. The collapse stops when the star
remnant is no longer able to support the self-similar infall feeding the
collisions. We shortly discuss possible astrophysical and cosmological
implications of these phenomena.
