Trapped surfaces due to concentration of gravitational radiation

Sequences of nonsingular, asymptotically flat initial data for general relativity (GR) in vacuo, called critical sequences, are defined which approach the strong-field limit of GR in a precise sense. It is proven that critical sequences contain trapped surfaces for large values of the argument. Thus, by a theorem due to Penrose, the spacetimes evolving from all such configurations must develop singularities. In the course of the proof a new and conceptually simple proof of the positivity of the Arnowitt-Deser-Misner mass in the strong-field regime is obtained.