GRAVITATIONAL-RADIATION, INSPIRALING BINARIES, AND COSMOLOGY

We show how to measure cosmological parameters using observations of inspiraling binary neutron star or black hole systems in one or more gravitational wave detectors. To illustrate, we focus on the case of fixed mass binary systems observed in a single Laser Interferometer Gravitational-wave Observatory (LIGO)-like detector. Using realistic detector noise estimates, we characterize the rate of detections as a function of a threshold signal-to-noise ratio rho0, the Hubble constant H-0, and the binary '' chirp '' mass. For rho0 = 8, H-0 = 100 km s-1 Mpc-1, and 1.4 M. neutron star binaries, the sample has a median redshift of 0.22. Under the same assumptions but independent of H-0, a conservative rate density of coalescing binaries (8 x 10(-8) yr-1 Mpc-3) implies LIGO will observe approximately 50 yr-1 binary inspiral events. The precision with which H-0 and the deceleration parameter q0 may be determined depends on the number of observed inspirals. For fixed mass binary systems, approximately 100 observations with rho0 = 10 in the LIGO detector will give H-0 to 10% in an Einstein-DeSitter cosmology, and 3000 will give q0 to 20%. For the conservative rate density of coalescing binaries, 100 detections with rho0 = 10 will require about 4 yr.