Computational astrophysics is a central part of modern, astronomical research. A small number of simple physical laws can give rise to an amazingly rich phenomenology, as the numerous observations of planetary, stellar, and galactic systems demonstrate so beautifully. The continuing increase in the speed and memory of computers allows us to perform ever more detailed simulations of complex astronomical phenomena, which can then be used to create "virtual observations". Such simulations are invaluable for testing theoretical models, for constraining the physical parameters of such models, and for gaining insight into the relative importance of different physical processes. Numerical simulations are also widely used for the design of observational campaigns, for testing data analysis software, and for revealing observational biases.
Computational astrophysics at Leiden Observatory covers a wide range of research fields. Activity is currently particularly high in the areas of radiative transfer (on scales ranging from planetary to cosmological and everything in between), hydrodynamical modelling of the formation of galaxies and of the evolution of the intergalactic medium, and the computation of detailed models for the internal dynamical structure of galaxies. Leiden researchers are regular users of a variety of computational facilities, ranging from local PC clusters to the high-performance systems at the national computing center.