Speaker:
　　　 Rainer Spurzem
Time:
　　　 Sept. 23rd, 2:00-3:00PM
Location:
　　　 3th floor, Large conf. room
Abstract:
We study the dynamical evolution of dense star clusters (globular clusters and galactic nuclei with single and binary supermassive black holes). Direct N-body simulations are compared with models based on statistical mechanics. It is shown that rotation accelerates the collisional dynamics of the system, and if Post-Newtonian relativistic forces between black holes are included, SMBH coalescence and gravitational wave emission is triggered after galaxy mergers. The treatment of relativistic corrections to Newtonian gravity is reviewed and we estimate gravitational wave amplitudes when the frequencies fall inside the band of the (planned) Laser Interferometer Space Antennae (LISA). In the second part of the talk our new computational instrument, is presented, a special supercomputer using graphical processing units (GPU) as accelerators, which is under construction at the National Astronomical Observatories of the Chinese Academy of Sciences in Beijing. We will also briefly review different kinds of special hardware (traditional GRAPE, FPGA, and GPU) and some implementation aspects (e.g. accuracy). We find in accord with previously published results of other groups that for N-Body simulations (real application codes) GPU hardware can be used with a very high efficiency and sustained speed, for low price. FPGA is more useful for complex pipelines (like SPH), where they reach much better efficiency and slightly better sustained speed than GPU. Finally in an outlook it is argued that future faster and larger generations of FPGA may provide comparable or even higher computing power than GPU with much less power consumption - so they are a promising path in the context of the new paradigm of 'Green Computing'.