Patrick Brady is interested in both theoretical and experimental gravitation. He is an Alfred P. Sloan Research Fellow and a Cottrell Scholar. His research interests include the the dynamics of gravitational collapse, black holes, numerical relativity including simulation of binary coalescence, and the detection of gravitational waves using interferometric gravitational-wave detectors.

The construction of LIGO, a national facility for detecting gravitational waves, is complete. The commissioning phase for the detectors has been in full swing for almost two years, and the first science data was collected August/September 2002. The analysis of this data is being organized by the LIGO Scientific Collaboration (LSC). Brady is a member of the LSC and co-chairs (with Gabriela Gonzalez, LSU) the inspiral analysis working group. This group is searching for gravitational-wave signals from binary systems as they spiral together by loss of energy as gravitational waves. LIGO is sensitive to the waves produced during the last few minutes of the inspiral just before the elements merge.

Along with other members of the LSC group at UWM, Brady contributes to working groups who look for unmodelled bursts and continuous signals like those that might be produced by rapidly rotating neutron stars. These activities reflect Brady's desire to move quickly towards scientific analysis of the data from gravitational-wave detectors. This role will continue over the next couple of years as the LIGO science data run begins and instrumental sensitivity improves. The prospects for interesting scientific investigations in this nascent field of gravitational wave astronomy are extant.

The natural progression from detection of gravitational waves to routine astronomical observations is the grail of gravitational-wave research. This involves a combination of theoretical and practical work in data analysis. The existence of black holes is among the most fascinating predictions of general relativity. Gravitational-wave astronomy promises to provide direct observation of strong gravitational fields around black holes while pairs of them are involved in violent relativistic interactions. Theoretical understanding of the late stages of inspiral and merger of black holes will be needed in order to extract physical information. Brady is also developing this research direction by becoming involved in the numerical computations of binary black hole inspiral and merger.

LISA, a proposed space-based gravitational-wave observatory, may fly towards the end of this decade. It will be sensitive to gravitational waves in frequency bands considerably lower than earth based interferometers. Space based interferometers will be sensitive to gravitational waves from neutron stars (or white dwarfs) spiraling into massive black holes. The optimal detection of the waves relies on knowing the waveform in advance. One method to determine the gravitational waves from these systems is to model the neutron star as a point particle orbiting a massive black hole and then compute the waves and their back reaction on the particles orbit. The point particle approximation introduces spurious divergences into this problem. With Anderson and Wiseman, I have used methods from quantum fields in curved spacetime to isolate the divergent part of the radiation reaction force on a particle orbiting a black hole. We are now developing the technique into a practical method to compute the radiation reaction force and subsequent motion of the particle. This approach is similar in spirit to that of Mino et al., and may provide a practical way to compute the orbital evolution of these extreme-mass-ratio binary systems.

Brady also remains interested in more abstract issues in gravitational theory. He continues the study of singularities and their formation in gravitational collapse. Numerical methods provide one of the best methods to examine broad, physically interesting parameter spaces of solutions involving singularities. Brady was a pioneer in using numerical schemes to study the null singularities inside black holes, and it remains open to extend these studies to realistic situations involving rotating holes.

More soon.