Scalar field black holes
  With a suitable decomposition of its energy-momentum tensor into pressureless
matter and a vacuum type term, we investigate the spherical gravitational
collapse of a minimally coupled, self-interacting scalar field, showing that it
collapses to a singularity. The formed blackhole has a mass $M \sim 1/m$ (in
Planck units), where $m$ is the mass of the scalar field. If the latter has the
axion mass, $m \sim 10^{-5}$ eV, the former has a mass $M \sim 10^{-5}
M_{\odot}$.
