Binary black hole mergers are the strongest expected producers of graviational radiation in the universe. Ground-based and proposed space-based gravitational wave detectors will benefit from simulations modeling the mergers and extracting the resulting gravitational waveforms. Producing templates of waveforms will both aid the likelihood of detection and the estimation of parameters (mass ratio, spin, etc.). openGR is modular, open framework development to carry out simulations of binary black hole mergers. While designed with the two-body problem in mind, openGR will evolve most general spacetimes. This work overviews the capabilities of openGR and the corresponding physics involved. openGR supports both excision and puncture methods. When excising the black hole, to date we have used only the weakly hyperbolic ADM formulation of the Einstein’s equations. As expected from a weakly hyperbolic system, instabilites arise and crash the code when simulating even just a single boosted black hole in Kerr-Schild coordinates. In contrast, successful mergers of two black holes have been achieved using the puncture method. We demonstrate such a simulation in Ch 8. In this case, we make use of a BSSN formulation of Einstein’s equations (a strongly hyperbolic system). / text

One of the most important predictions of General Relativity, Einstein’s theory of gravity, is the existence of gravitational radiation. The strongest source of such radiation is expected to come from the merging of black holes. Upgrades to large ground based interferometric detectors (LIGO, VIRGO, GEO 600) have increased their sensitivity to the point that the first direct observation of a gravitational wave is expected to occur within the next few years. The chance of detection is greatly improved by the use of simulated waveforms which can be used as templates for signal processing. Recent advances in numerical relativity have allowed for long stable evolution of black hole mergers and the generation of expected waveforms. openGR is a modular, open framework black hole evolution code developed at The University of Texas at Austin Center for Relativity. Based on the BSSN (strongly hyperbolic) formulation of Einstein’s equations and the moving puncture method, we are able to model the evolution of a binary black hole system through the merger and extract the gravitational radiation produced. Although we are generally interested in binary interactions, openGR is capable of handling any number of black holes. This work serves as an overview of the capabilities of openGR and a demonstration of the physics it can be used to explore. / text