Matter flows around black holes and gravitational radiation - art. no. 044014

We develop and calibrate a new method for estimating the gravitational radi ation emitted by complex motions of matter sources in the vicinity df black holes. We compute numerically the linearized curvature perturbations induc ed by matter fields evolving in fixed black hole backgrounds, whose evoluti on we obtain using the equations of relativistic hydrodynamics. The current implementation of the proposal concerns Schwarzschild black holes and axis ymmetric hydrodynamical motions. As first applications we study (i) dust sh ells falling onto the black hole isotropically from finite distance, (ii) i nitially spherical layers of material falling onto a moving black hole, and (iii) anisotropic collapse of shells. We focus on the dependence of the to tal gravitational wave energy emission on the flow parameters, in particula r shell thickness, velocity and degree of anisotropy. The gradual excitatio n of the black hole quasi-normal mode frequency by sufficiently compact she lls is demonstrated and discussed. A new prescription for generating physic ally reasonable initial data is discussed, along with a range of technical issues relevant to numerical relativity. [S0556-2821(99)05602-7].