Gravitational collapse and formation of universal horizons in
  Einstein-aether theory
  We numerically study the gravitational collapse of a massless scalar field
with spherical symmetry in Einstein-aether theory, and show that apparent,
spin-0 and dynamical universal horizons (dUHs) can be all formed. The spacetime
and the aether field are well-behaved and regular, including regions nearby
these horizons (but away from the center of spherical symmetry). The spacetime
outside the apparent and spin-0 horizons settles down to a static
configuration, and some of such resulting static black holes were already found
numerically in the literature. On the other hand, the proper distance of the
outermost dUH from the apparent (or spin-0) horizon keeps increasing on
$\mbox{\ae}$ther-orthogonal time slices. This indicates that the outermost dUH
is evolving into the causal boundary, even for excitations with large speeds of
propagation.
