Evolution of circular, nonequatorial orbits of Kerr black holes due to gravitational-wave emission. II. Inspiral trajectories and gravitational waveforms

Scott A. Hughes
Phys. Rev. D 64, 064004 – Published 24 August 2001
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Abstract

The inspiral of a “small” (μ1100M) compact body into a “large” (M1057M) black hole is a key source of gravitational radiation for the space-based gravitational-wave observatory LISA. The waves from such inspirals will probe the extreme strong-field nature of the Kerr metric. In this paper, I investigate the properties of a restricted family of such inspirals (the inspiral of circular, inclined orbits) with an eye toward understanding observable properties of the gravitational waves that they generate. Using results previously presented to calculate the effects of radiation reaction, I assemble the inspiral trajectories (assuming that radiation reacts adiabatically, so that over short time scales the trajectory is approximately geodesic) and calculate the wave generated as the compact body spirals in. I do this analysis for several black hole spins, sampling a range that should be indicative of what spins we will encounter in nature. The spin has a very strong impact on the waveform. In particular, when the hole rotates very rapidly, tidal coupling between the inspiraling body and the event horizon has a very strong influence on the inspiral time scale, which in turn has a big impact on the gravitational wave phasing. The gravitational waves themselves are very usefully described as “multi-voice chirps”: the wave is a sum of “voices,” each corresponding to a different harmonic of the fundamental orbital frequencies. Each voice has a rather simple phase evolution. Searching for extreme mass ratio inspirals voice-by-voice may be more effective than searching for the summed waveform all at once.

  • Received 13 April 2001

DOI:https://doi.org/10.1103/PhysRevD.64.064004

©2001 American Physical Society

Authors & Affiliations

Scott A. Hughes

  • Institute for Theoretical Physics, University of California, Santa Barbara, California 93103
  • Theoretical Astrophysics, California Institute of Technology, Pasadena, California 91125

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Issue

Vol. 64, Iss. 6 — 15 September 2001

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