Black hole formation by incoming electromagnetic radiation
  I revisit a known solution of the Einstein field equations to show that it describes the formation of non-spherical black holes by the collapse of pure electromagnetic monochromatic radiation. Both positive and negative masses are feasible without ever violating the dominant energy condition. The solution can also be used to model the destruction of naked singularities and the evaporation of white holes by emission or reception of light. 
Jos\'e M. M. Senovilla
gr-qc hep-th