Gravitational waves have become a very hot topic in astrophysics since their detection by LIGO in 2015. This means that also possible precursors are in the focus of research – general relativistic research because these objects are either black holes or neutron stars. The 2017 Biermann Lecturer, Masaru Shibata from the Kyoto University, uses numerical simulations and general relativity (or numerical relativity for short) to study the merger of such extreme objects and the properties of both the electromagnetic radiation and gravitational waves emitted during these events.