Numerical Relativity  concerns the modeling and simulation of some of the most extreme astrophysical events in the Universe, such as colliding black-holes and neutron stars, which are known to generate intense burst gravitational and electromagnetic radiation.

The violence of the collision among two black holes, for example, whips space itself into wild vibrations, called Gravitational Waves, which race outwards from the collision with the speed of light (see Figure), carrying huge amounts of energy. Gamma ray bursts (unexplained blasts of intense electromagnetic radiation), and other phenomena such as jets in active galactic nuclei are also believed to be associated with black holes.

The past few years have witnessed several breakthroughs in numerical relativity, and the four decades old problem of simulating the coalescence of black-hole binaries in fully relativistic, strong-field gravity, which is described by Einstein's theory of General Relativity, has now been solved opening new frontiers in gravitational astrophysics.

In particular, the moving punctures approach, inroduced by CCRG group members has already produced many interesting calculations and predictions on dynamical phenomena that result from the emission of gravitational radiation in the final stages of the mergers of two or more black holes. Among these results is the discovery of large gravitational-radiation recoils (up to 4000 km/s) from spinning supermassive black hole binaries, the study of spin dynamics effects, such as spin-flips, precession and hang-up orbits.

Some of these results may produce significant electromagnetic signatures in active galactic nuclei (AGNs) and hence be relevant for the interpretation and analysis of astronomical observational data.

General Relativistic Magneto-Hydrodynamics simulations  and other numerical hydrodynamics techniques, typically used in fluid dynamics, are used in the context of general relativity to model these phenomena and other phenomena.

This research is supported by NSF grants PHY-0722315, PHY-0653303, PHY-0714388, and PHY-0722703 and a NASA grant 07-ATFP07-0158.

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