Black hole formation through fragmentation of toroidal polytropes
  We investigate new paths to black hole formation by considering the general relativistic evolution of a differentially rotating polytrope with toroidal shape. We find that this polytrope is unstable to nonaxisymmetric modes, which leads to a fragmentation into self-gravitating, collapsing components. In the case of one such fragment, we apply a simplified adaptive mesh refinement technique to follow the evolution to the formation of an apparent horizon centered on the fragment. This is the first study of the one-armed instability in full general relativity. 
Burkhard Zink, Nikolaos Stergioulas, Ian Hawke, Christian D. Ott, Erik   Schnetter and Ewald Mueller