ADM and Bondi four-momenta for the ultrarelativistic Schwarzschild black   hole
  We argue that it is possible to assign Bondi as well as ADM four-momentum to the ultrarelativistic limit of the Schwarzschild black hole in agreement to what is expected on physical grounds: The Bondi-momentum is lightlike and equal to the ADM-momentum up to the retarded time when particle and radiation escape to infinity and drops to zero thereafter, leaving flat space behind. 
P.C. Aichelburg (University of Vienna), H. Balasin (TU-Wien)