Characterizing astrophysical sources of gravitational waves

Abstract

The Laser Interferometer Space Antenna (LISA) and the Laser Interferometer Gravitational-wave Observatory (LIGO) are designed to detect gravitational waves from a wide range of astrophysical sources. The parameter estimation ability of these detectors can be determined by simulating the response to predicted gravitational wave sources with instrument noise and searching for the signals with sophisticated data analysis methods. A possible source of gravitational waves will be beams of radiation from discontinuities on cosmic length strings. Cosmic strings are predicted to form kinks and cusps that travel along the string at close to the speed of light. These disturbances are radiated away as highly beamed gravitational waves that produce a burst-like pulse as the cone of emission sweeps past an observer. The detection of a gravitational wave signal from a cosmic string cusp would illuminate the fields of string theory, cosmology, and relativity. Gravitational wave sources also include coalescing binary systems of compact objects. Colliding galaxies have central black holes that sink to the center of the merged galaxy and begin to orbit one another and emit gravitational waves. Previous LISA data analysis studies have assumed that binary black hole systems have a circular orbit or an extreme mass ratio. It is ultimately necessary to understand the general case of spinning black hole binary systems in eccentric orbits and how LISA observations can be used to measure the eccentricity of the orbits as well as the masses, spins, and luminosity distances of the black holes. Once LISA is operational, the comparison of observations of eccentric and circular black hole binary sources will constrain theories on galaxy mergers in the early universe.