Figure 1: Artist’s conception of a pulsar timing array. The gravitational wave background, depicted as a warping of the grid in this image, induces correlated timing variations in pulsars distributed throughout space.

The Race to Detect Gravitational Waves: Pulsar Timing Arrays

By Chris Faesi
November 23, 2012

Paper: The imminent detection of gravitational waves from massive black-hole binaries with pulsar timing arrays

Authors: Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorious

First Author’s Institution: Princeton University Dept. of Physics

The Era of Gravitational Wave Astronomy

The detection of gravitational waves is one of the next major frontiers in physics. Predicted by Einstein’s general theory of relativity but not yet directly confirmed experimentally, many cutting-edge facilities have been and are being built with the singular goal of discovering their existence. It is possible, however, that an Earth-based experiment will not be the first to confirm gravitational waves. Instead, astrophysicists using pulsar timing arrays – Galaxy-wide networks of spinning neutron stars – may be on the verge of this groundbreaking discovery. In today’s paper, the authors argue that new calculations for the number of supermassive black hole mergers – a prime source of gravitational waves – imply a signal that may be measurable by pulsar timing arrays with current data.

What are Gravitational Waves?

According to general relativity (GR), the presence of matter causes the fabric of spacetime to curve, and the motion of massive objects causes this curvature to change with time. GR predicts that an accelerating object should radiate gravitational waves (GWs), just like how an accelerating charge radiates electromagnetic waves. Gravitational waves are essentially “disturbances” in the fabric of spacetime; the effect of a passing GW on a circle of stationary test masses is to cause them to oscillate orthogonally, with the particles along one axis and then the other being displaced alternately inward; see this animation for a nice visualization of the effect. Since gravity is much, much weaker than the other fundamental forces of nature, gravitational waves have incredibly small amplitudes. Even from the strongest sources of GWs, the effect on test masses is expected to be so small as to be almost unmeasurable.

Read more: The Race to Detect Gravitational Waves: Pulsar Timing Arrays | astrobites.

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