Parallelization, Special Hardware and Post-Newtonian Dynamics in Direct N - Body Simulations

The formation and evolution of supermassive black hole (SMBH) binaries during and after galaxy mergers is an important ingredient for our understanding of galaxy formation and evolution in a cosmological context, e.g. for predictions of cosmic star formation histories or of SMBH demographics (to predict events that emit gravitational waves). If galaxies merge in the course of their evolution, there should be either many binary or even multiple black holes, or we have to find out what happens to black hole multiples in galactic nuclei, e.g. whether they come sufficiently close to merge resulting from emission of gravitational waves, or whether they eject each other in gravitational slingshot interactions

A pilgrimage to gravity on GPUs

In this short review we present the developments over the last 5 decades that have led to the use of Graphics Processing Units (GPUs) for astrophysical simulations. Since the introduction of NVIDIA's Compute Unified Device Architecture (CUDA) in 2007 the GPU has become a valuable tool for N-body simulations and is so popular these days that almost all papers about high precision N-body simulations use methods that are accelerated by GPUs. With the GPU hardware becoming more advanced and being used for more advanced algorithms like gravitational tree-codes we see a bright future for GPU like hardware in computational astrophysics.Comment: To appear in: European Physical Journal "Special Topics" : "Computer Simulations on Graphics Processing Units" . 18 pages, 8 figure

Up to 700k GPU Cores, Kepler, and the Exascale Future for Simulations of Star Clusters Around Black Holes

We present benchmarks on high precision direct astrophysical N-body simulations using up to several 100k GPU cores; their soft and strong scaling behaves very well at that scale and allows further increase of the core number in the future path to Exascale computing. Our simulations use large GPU clusters both in China (Chinese Academy of Sciences) as well as in Germany (Judge/Milkyway cluster at FZ Julich). Also we present first results on the performance gain by the new Kepler K20 GPU technology, which we have tested in two small experimental systems, and which also runs in the titan supercomputer in the United States, currently the fastest computer in the world. Our high resolution astrophysical N-body simulations are used for simulations of star clusters and galactic nuclei with central black holes. Some key issues in theoretical physics and astrophysics are addressed with them, such as galaxy formation and evolution, massive black hole formation, gravitational wave emission. The models have to cover thousands or more orbital time scales for the order of several million bodies. The total numerical effort is comparable if not higher than for the more widely known cosmological N-body simulations. Due to a complex structure in time (hierarchical blocked time steps) our codes are not considered 'brute force'. ? 2013 Springer-Verlag.EI