Colliding black holes from a null point of view: the close limit
  We present a characteristic algorithm for computing the perturbations of a Schwarzschild spacetime by means of solving the Teukolsky equations. Our methods and results are expected to have direct bearing on the study of binary black holes presently underway using a fully {\em nonlinear} characteristic code \cite{Gomez98a}. 
Sascha Husa, Manuela Campanelli, Roberto Gomez, Jeffrey Winicour and   Yosef Zlochower