Golden Binary Gravitational‐Wave Sources: Robust Probes of Strong‐Field Gravity

Space-born gravitational-wave interferometers such as {\it LISA} will detectthe gravitational wave (GW) signal from the inspiral, plunge and ringdownphases of massive black hole binary mergers at cosmological distances. From theinspiral waves, we will be able to measure the masses of the binaries' members;from the ringdown waves, we will be able to measure the mass of the finalmerged remnant. A subset of detected events allow the identification of boththe inspiral and the ringdown waveforms in a given source, and thus allow ameasurement of the total mass-energy lost to GWs over the coalescence, $M_{\rmGW}$. We define ``golden'' binary mergers to be those with measurement errorslikely to be small enough for a physically useful determination of $M_{\rmGW}$. A detailed sensitivity study, combined with simple black hole populationmodels, suggests that a few golden binary mergers may be detected during a3-year {\it LISA} mission lifetime. Any such mass deficit measurement wouldconstitute a robust and valuable observational test of strong-fieldrelativistic gravity. An extension of this concept to include spin measurementsmay allow a direct empirical test of the black hole area theorem.Comment: 18 pages, 6 figures. Accepted for publication in Ap