The Max Planck Institute for Gravitational Physics is one of the four partners in the international consortium GWSky, which the European Research Council has awarded 12 million euros to develop a deeper understanding of gravitational waves. Existing and future gravitational-wave detectors will be capable of observing signals with such precision that they may reveal possible deviations from Einstein’s general theory of relativity and the standard model of particle physics. To fully exploit this unique instrumental capability, fundamental advances are required in the theoretical description of black holes and their dynamics, the gravitational waves they emit, their cosmic environment, and the physics beyond the standard model. To provide the necessary theoretical…