Geometry of conformally symmetric generalized Vaidya spacetimes

In this paper, we consider conformally symmetric generalized Vaidya spacetimes with a composite null dust and null string matter distribution using the semi-tetrad covariant 1 + 1 + 2 decomposition method. The important and novel result that emerges from our analysis is that all the geometric variables related to the time-like and the preferred space-like congruences are completely determined by the conformal vector and conformal factor. This result is unique to the specific matter distribution of the generalized Vaidya configuration. We further show that in the case of the pure null dust (or Vaidya) spacetime, a proper conformal Killing vector cannot be admitted.