Matching spherical dust solutions to construct cosmological models

Conditions for smooth cosmological models are set out and applied to inhomo geneous spherically symmetric models constructed by matching together diffe rent Lemaitre-Tolman-Bondi solutions to the Einstein field equations. As an illustration the methods are applied to a collapsing dust sphere in a curv ed background, This describes a region which expands and then collapses to form a black hole in an Einstein de Sitter background. We show that in all such models if there is no vacuum region then the singularity must go on ac creting matter for an infinite LTB time.