Coalescing binaries—Probe of the universe

Abstract

At present, coalescing binary systems containing neutron stars or black holes are thought to be the most likely sources of gravitational waves to be detected by long baseline interferometers being currently designed. In this essay we calculate the characteristics of the signal from a coalescing binary to the first post-Newtonian order. We show that at coalescence the eccentricity of the orbit, tidal effects, and magnetic interactions can be neglected. We also consider the effects of the expansion of the universe on the signal. We show that observations of gravitational waves from coalescing binaries by a network of detectors will provide a wealth of astrophysical information, e.g., determination of the Hubble constant, new rungs on the cosmic distance ladder, estimates of the masses of components of the binary systems, information about the mass distribution in the universe, highly accurate tests of general relativity, and constraints on neutron-star equations of state. Further development of laser interferometers may enable determination of the deceleration parameter, provide new information about evolution of the universe, and even enable observation of such effects as gravitational lensing.