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Detectors
Published in C. R. Kitchin, Astrophysical Techniques, 2020
One suggested approach to detecting low-frequency gravitational waves is to use the Gaia spacecraft’s (or some similar future mission’s) data to look for changes in star’s positions (i.e., their proper motions). The star positions would change as the gravitational wave passed through the Earth. Although the change for an individual star would be small and lost in the noise, the wave would cause all the observed stars’ positions to change in a regular pattern depending upon the nature of the gravitational disturbance and so might be detectable. Since Gaia would have to measure many star positions at least twice, only slow changes would be detectable; Gaia’s first and second data releases took three and five years, respectively, to appear after its launch. The method would thus not detect rapid events like GW150914 but might detect components of the cosmic gravitational wave background.
Geometric theory of topological defects: methodological developments and new trends
Published in Liquid Crystals Reviews, 2021
Sébastien Fumeron, Bertrand Berche, Fernando Moraes
Cosmic wedge disclinations exist either as stable infinite straight lines (their equation of state simply equates the string energy density to its tension ) or as closed loops that radiate away gravitational waves until they vanish. When moving, strings happen to distort spacetime such that at all scales, matter accretes along its wake into sheet-like structures. They may account for the formation of large-scale structures in our universe (including the Great Wall) and they have several expected observable signatures such as the Kaiser-Stebbins effect [91,92] (an asymmetric Doppler shift giving rise to anisotropies of the cosmic microwave background), gravitational lensing [93] (not in the form of an Einstein ring, but as a double image instead), geometric phase (Aharonov-Bohm effect but with a cosmic string replacing the flux tube [94])…Up to now, data collected by the PLANCK mission (2014) only settle upper bounds on the string parameter μ [95] and in 2020, observations of the stochastic gravitational wave background (NANOGrav experiment) may have provided with first evidence for cosmic strings [96–98].