Cosmological Gravitational Wave Background Research Articles

Clustering correlations and limits on cosmological gravitational waves

A cosmological background of gravitational waves induces angular deviations in the propagation of light traversing it. All observed astrophysical sources might therefore have varying apparent positions, with the time dependence set by the wave period. Wavelengths greater than a kiloparsec are examined, so the positions are frozen but in general correlated. Comparison with observed galaxy-galaxy n-point correlation functions provide a spectrum-independent limit on the energy density of gravitational waves with wavelengths between a few tens of kiloparsecs and a few hundred megaparsecs of Omega(GW) less than 0.001.

Microwave background anisotropy induced by gravitational waves

A cosmological background of gravitational waves induces redshift perturbations in light transversing it. Calculations of this Sachs-Wolfe effect on the microwave background are presented in an Omega = 1 Friedmann universe as a function of angular scale and gravitational wave spectrum. Blurriness of the last-scattering surface can cause nonnegligible dilution of the anisotropy for wavelengths less than about 100 Mpc. The limit implied for the energy density of the gravitational waves is given. A difficulty in associating a linear scale with an angular anisotropy, due to the clumpiness of the universe, is also pointed out.

Relativistic scattering coherence.

Wave propagation through inhomogeneous, turbulent media is investigated for the case where the signal and inhomogeneities move relativistically. Although in classical treatments the mean-square angular deviations grow as the path length, this is found not to be true relativistically. Special attention is given to the problem of light propagating through a cosmological background of gravitational waves.

Gravitational waves and cosmology

The strong bursts of gravitational waves detected by Weber, if confirmed, suggest the presence in the Galaxy of arelativistic cluster of collapsed bodies which «burns» its own gravitational potential energy and slowly decays into a dead, collapsed object. We discuss the possibility of this being a common feature throughout the universe and consider a simple cosmological model in which the «missing mass» is attributed mainly to gravitational waves and dead, dark galaxies. The production of the former is described by a simple rate equation containing a characteristic frequency α. Using the known value of the Hubble constantH and the present visible mass density we find, when the efficiency of the process is, say, 0.5, α≈8H; the corresponding gravitational brightness of an average galaxy turns out to agree with Weber's figure (assuming a wide-band spectrum) to within a factor 2. This model features an isotropic cosmological background of gravitational waves, with energy density about 50 times smaller than the energy arriving from the galactic nucleus.