It is well known that gravitational waves interact in a non-linear way. This makes it difficult to describe them rigorously. The cleanest description is based on a certain conformal invariance of the Einstein equations - a fact which was established by R. Penrose and was used by H. Friedrich to prove several important global results for general relativistic space-times. The so-called conformal field equations implement this conformal invariance on the level of partial differential equations. They provide various well-posed initial (boundary) value problems for use in different situations. The talk will give a computational perspective on the non-linear interaction of gravitational waves with an initially static (and spherically symmetric) black hole. We will show how to kick it and possibly how to spin it up. Time permitting, we will also discuss the emergence of quasi-normal modes and the Newman-Penrose constants.
Jörg Frauendiener (New Zealand): How to kick a black hole
