DYNAMICS OF BLACK-HOLE APPARENT HORIZONS

Dynamic black hole spacetimes are studied by examining the evolution o f apparent horizons surrounding the holes. We performed numerical evol utions of three different initial data sets: nonrotating black holes d istorted by time symmetric (Brill) gravitational waves, distorted rota ting black holes, and the time symmetric two black hole Misner data. A lthough the initial data sets represent different physical problems, t he results for these systems are strikingly similar. At early times in the evolution, the apparent horizons may be very distorted and nonsph erical (or disjoint in the case of two black holes), but the systems q uickly settle down to a nearly spherical or oblate (in the case of rot ating holes) configuration and the horizons are then seen to oscillate at the quasinormal frequency of the final black hole. In the case of two black holes with disjoint horizons, we see the appearance of a lar ger horizon surrounding both holes as they collide. From this point th e horizon dynamics is very similar to the single distorted black hole systems. The wavelength and damping time of the quasinormal modes and the rotation parameter in the rotating cases can be read off directly from oscillations in the geometry of the black hole horizons. The appa rent horizon is thus shown to be a powerful tool in the study of black hole spacetimes.