The characteristic treatment of black holes

The characteristic initial value problem has been implemented as a robust computational algorithm (the PITT NULL CODE), with direct application to binary black holes. The event horizon can be analyzed by characteristic techniques as a stand-alone object using an analytic conformal model which gives new insight into the intrinsic geometry of binary black holes. When applied to a non-axisymmetric horizon, the model reveals substantially new features. Colliding black holes generically go through a toroidal phase before they become spherical. The conformal structure of the horizon supplies part of the data for a simulation of the exterior space-time and calculation of the post-merger waveforms from a binary black hole inspiral.