The role of anisotropy and inhomogeneity in Lemaitre-Tolman-Bondi   collapse
  We study the effects of shear and density inhomogeneities in the formation of naked singularities in spherically symmetric dust space--times. We find that in general neither of these physical features alone uniquely specifies the end state of the gravitational collapse. We do this by (i) showing that, for open sets of initial data, the same initial shear (or initial density contrast) can give rise to both naked and covered solutions. In particular this can happen for zero initial shear or zero initial density contrast; (ii) demonstrating that both shear and density contrast are invariant under a one parameter set of linear transformations acting on the initial data set and (iii) showing that asymptotically (near the singularities) one cannot in general establish a direct relationship between the rate of change of shear (or density contrast) and the nature of the singularities. However, one can uniquely determine the nature of the singularity if both the initial shear and initial density contrast are known.   These results are important in understanding the effects of the initial physical state and in particular the role of shear, in determiming the end state of the gravitational collapse. 
Filipe C. Mena (Oxford/Minho), Brien C. Nolan (DCU, Dublin) and Reza   Tavakol (QM, London)