EVENT HORIZONS IN NUMERICAL RELATIVITY - METHODS AND TESTS

This is the first paper in a series on event horizons in numerical rel ativity. In this paper we present methods for obtaining the location o f an event horizon in a numerically generated spacetime. The location of an event horizon is determined based on two key ideas: (1) integrat ing backward in time and (2) integrating the whole horizon surface. Th e accuracy, efficiency and robustness of the methods are examined with various sample spacetimes, including both analytic (Schwarzschild and Kerr) and numerically generated black holes. The numerically evolved spacetimes contain highly distorted black holes, rotating black holes, and colliding black holes. In all cases studied, our methods can find event horizons to within a very small fraction of a grid zone.