Self-gravitating system made of axions
  We show that the inclusion of an axion-like effective potential in the
construction of a self-gravitating system made of scalar fields leads to a
decrease on its compactness when the value of the self-interaction coupling
constant is increased. By including the current values for the axion mass m and
decay constant f_a, we have computed the mass and the radius for
self-gravitating systems made of axion particles. It is found that such objects
will have asteroid-size masses and radius of few meters, then, the
self-gravitating system made of axions could play the role of scalar
mini-machos that are mimicking a cold dark matter model for the galactic halo.
