A universal inequality between angular momentum and horizon area for   axisymmetric and stationary black holes with surrounding matter
  We prove that for sub-extremal axisymmetric and stationary black holes with arbitrary surrounding matter the inequality $8\pi|J|<A$ holds, where $J$ is the angular momentum and $A$ the horizon area of the black hole. 
J\"org Hennig, Marcus Ansorg and Carla Cederbaum