On the electromagnetic field of a charged collapsing spherical shell in   general relativity
  A new exact solution of the Einstein-Maxwell equations for the gravitational collapse of a shell of matter in an already formed black hole is given. Both the shell and the black hole are endowed with electromagnetic structure and are assumed spherically symmetric. Implications for current research are outlined. 
Christian Cherubini, Remo Ruffini, Luca Vitagliano