Gravitational Radiation, Inspiraling Binaries, and Cosmology

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Session 67 -- Cosmology and Distance Indicators
Oral presentation, Thursday, January 13, 2:15-3:45, Crystal Forum Room (Crystal City Marriott)

[67.05] Gravitational Radiation, Inspiraling Binaries, and Cosmology

L.S.Finn (Northwestern University), D.F.Chernoff (Cornell University)

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 $\rho_0$, the Hubble constant $H_0$, and the binary ``chirp'' mass. For $\rho_0 = 8$, $H_0 = 100\,\mbox{km s}^{-1} \mbox{Mpc}^{-1}$, and $1.4 \mbox{M}_{\sun}$ neutron star binaries, the anticipated sample has a median redshift of $0.22$. Under the same assumptions but independent of $H_0$, a conservative rate density of coalescing binaries ($8\times10^{-8} \,\mbox{yr}^{-1} \,\mbox{Mpc}^{-3}$) implies LIGO will observe $\sim 50\,\mbox{yr}^{-1}$ binary inspiral events.

The precision with which $H_0$ and the deceleration parameter $q_0$ may be determined depends on the number of observed inspirals. For fixed mass binary systems, $\sim 100$ observations with $\rho_0 = 10$ in the LIGO detector will give $H_0$ to 10\% in an Einstein-DeSitter cosmology, and 3000 will give $q_0$ to 20\%. For the conservative rate density of coalescing binaries, 100 detections with $\rho_0 = 10$ will require about 4~yrs.

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