The spacetime outside a source of gravitational radiation: The axially
  symmetric null fluid
  We carry out a study of the exterior of an axially and reflection symmetric
source of gravitational radiation. The exterior of such a source is filled with
a null fluid produced by the dissipative processes inherent to the emission of
gravitational radiation, thereby representing a generalization of the Vaidya
metric for axially and reflection symmetric spacetimes. The role of the
vorticity, and its relationship with the presence of gravitational radiation is
put in evidence. The spherically symmetric case (Vaidya) is, asymptotically,
recovered within the context of the $1+3$ formalism.
