This award will support a research program at Princeton University, which is focused on understanding the strong-field regime of Einstein's theory of general relativity. Projects that will be pursued include modeling sources of gravitational waves in the universe (in particular collisions of compact objects such as black holes and neutron stars), high-speed black hole collisions, gravitational collapse, the interior structure of black holes, and the nature of gravity in a universe with extra dimensions. An integral part of the research program will also be to provide a vehicle to efficiently educate students in the methodology and process of performing fundamental scientific research via computer simulation. This will be achieved through development of a series of self-contained computational physics projects with interactive web-based interfaces; undergraduate or beginning graduate students will be able to work through the projects to write and use fully functional simulation codes of simplified model problems, while high-school level students will be able to use the web interface to explore working versions of the simulations. The research could have broader impact in several areas. First, knowledge of the structure of the gravitational waves radiated in compact object collisions will form an integral part of identifying and understanding such events, should they occur in the universe and be seen by a new generation of gravitational wave observatories. Second, studies of solutions of the equations of general relativity in the dynamical strong field regime should provide much insight into the nature of this enigmatic theory in extreme conditions. Furthermore, if the universe happens to contain extra dimensions, black holes might be produced in high energy particle accelerators or in cosmic ray collisions with the earth's atmosphere, and knowledge of general relativity in extreme conditions could help in identifyng and understanding such events. Finally, the importance of computer simulation in fundamental and applied scientific research will continue to grow in coming years, and the educational tools that this research program will produce should be of significant benefit in training the next generation of scientists and engineers.
Over the 5 year period of the award, significant advances in our understanding of the strong-field dynamics of Einstein's theory of general relativity were made by the PI and his group. The primary accomplishments include (1) a new understanding of the nature of gravitational waves emitted during the merger of black hole/neutron star and binary neutron star systems that have large orbital eccentricity, (2) invention of a new methodology to use future gravitational wave observations to test how well Einstein's theory does in fact describe black hole mergers, or if not allow the discovery of new physics, (3) development of a new numerical method to study the tidal disruption of a star by a super-massive black hole, (4) the first numerical studies of the high speed limit of particle collision, showing that they can form black holes, (5) simulations that demonstrate higher dimensional black holes and black strings can exhibit behavior strikingly analogous to low viscosity fluid flows. In total, over the 5 years the group included the participation of 6 postdoctoral researchers, 4 graduate students and 12 undergraduate students. They were exposed to and taught how to do cutting edge scientific research, trained in high performance computing methods and how to utilize modern compute clusters, and learned how to disseminate results through publication in journals and speaking at conferences. Several of the undergraduates developed web-based tutorials on basic numerical methods for solving the kinds of equations relevant to not only Einstein's equations, but also computational fluid dynamics and related problems. This could be of significant value to beginning students who wish to learn about computational modeling.
