On the growth of massive scalar hair around a Schwarzschild black hole
  Through numerical simulations of a minimally coupled massive Klein-Gordon
scalar field, we show that it is possible to grow hair on a Schwarzschild black
hole if one assumes an initial periodically time-varying but spatially
homogeneous scalar background. By "hair", we mean a non-trivial profile in the
scalar field. We find that this profile emerges on a timescale related to the
mass of the black hole, with features related to the mass of the scalar
particle. We undertake simulations with and without backreaction on the metric
and see that the essential, qualitative features remain consistent. We also
contrast the results from higher mass scalars to the case of a low mass with a
large Compton wavelength. The results are particularly relevant for
scalar-tensor theories of gravity and dark matter models consisting of a
massive scalar, e.g. axions.
