Session H1 - Issues in Gravitational Radiation.
INVITED session, Sunday morning, April 29
Grand Ballroom North/Central, Renaissance Hotel$

[H1.001] Gravitational Radiation Instabilities in Rotating Neutron Stars

Gravitational radiation drives an instability in the r-modes of rotating stars. This instability is strong enough to cause the amplitude of these modes to grow on a timescale of tens of seconds in rapidly rotating neutron stars. Gravitational radiation emitted by these modes removes angular momentum from the star, causing it to spin down to a relatively small angular velocity on a timescale thought to be about one year. I will discuss at a pedagogical level the mechanism of gravitational radiation instability in rotating stars, the r-modes, and our present understanding of the competing dissipation mechanisms in neutron stars. I will also discuss the astrophysical implications of this mechanism for young neutron stars, and for older systems such as low mass x-ray binaries. Our current understanding of the prospects for directly detecting the gravitational radiation emitted during a spindown event will also be discussed.

[H1.002] Computing the Complete Gravitational Wavetrain from Relativistic Binary Inspiral

We present a new method for generating the nonlinear gravitational wavetrain from the late inspiral (pre-coalescence) phase of a binary neutron star system by means of a numerical evolution calculation in general relativity. In a prototype calculation, we produce 214 wave cycles from corotating polytropes, representing the final part of the inspiral phase prior to reaching the ISCO. Our method is based on the inequality that the orbital decay timescale due to gravitational radiation is much longer than an orbital period and the approximation that gravitational radiation has little effect on the structure of the stars. We employ quasi-equilibrium (QE) sequences of binaries in circular orbit for the matter source in our field evolution code. We compute the gravity-wave energy flux, and, from this, the inspiral rate, at a discrete set of binary separations. Using these data, we construct the gravitational waveform as a continuous wavetrain. We conclude that the QE scheme provides a promising technique for constructing the complete wavetrain from binary inspiral outside the ISCO, where the fields are strong but where following the system for more than a few orbits by direct numerical integration of the exact equations is prohibitive. We discuss the limitations of our current calculation, planned improvements, and potential applications of our QE method to other inspiral scenarios. A video highlighting key features of our calculation will be shown.

[H1.003] Gravitational Radiation and Equations of Motion: Post-Newtonian Methods

The completion of a network of advanced laser-interferometric gravitational-wave observatories around 2001 will make possible the study of the inspiral and coalescence of binary systems of compact objects (neutron stars and black holes), using gravitational radiation. To extract useful information from the waves, theoretical general relativistic gravitational waveforms will be used as templates, cross-correlated against the detector outputs. The templates must be extremely accurate, probably as accurate as O[(v/c)^6] beyond the predictions of the simple quadrupole formula. This presents a major challenge to theorists. We summarize a new method for calculating gravitational radiation to high order in v/c, in which Einstein's equations are recast as a flat spacetime wave equation with matter source and gravitational non-linearities extending to infinity. The method is free of divergences and properly yields non-linear effects, such as ``tails''. We report on progress in evaluating equations of motion to third post-Newtonian order, and in obtaining radiation reaction effects of spinning bodies.

[H1.004] Gravitational radiation reaction in strong fields

Solar-mass compact objects in orbital motion around massive black holes emit low-frequency gravitational waves that can be measured by a space-based interferometric detector such as LISA (Laser Interferometer Space Antenna). The detailed modeling of these sources, to the extent that templates could be provided for data analysis, requires a detailed computation of the motion over a very large number of orbital cycles. This, in turn, requires a detailed understanding of radiation-reaction effects in strong gravitational fields. I will review some of the recent work on this topic, starting with the foundational aspects and concluding with concrete applications.

[H1.005] Separating Gravitational-Wave Signals from Detector Noise

Part H of program listing