Catching a (Gravitational) Wave

September 16, 2009

Einstein’s theory of General Relativity says that the phenomenon we observe as gravity is the effect  of curvature of space-time due to the presence of mass.  This idea has a number of implications: for example, it implies that light should be bent when passing through a strong gravitational field  (so-called gravitational lensing), a prediction that has been verified by experiment.  The theory also predicts the existence of gravitational waves, but so far, there is only indirect evidence for their existence.  As you might guess, these waves occur at very low frequency (micro Hertz to nano Hertz), and have corresponding very long wavelengths.

According to a note posted on the “Physics arXiv Blog” at the Technology Review web site, a group of astronomers has come up with a new method of looking for these waves, by looking for their effect on the observed radiation from other objects:

Gravitational waves should also stretch and squeeze pulsars as they pass by, subtly changing the radio pulses they produce. So by monitoring an array of pulsars throughout the galaxy, astronomers should be able to see the effects of nanohertz to microhertz gravitational waves passing by. The array of pulsars should effectively shimmer as the waves wash over it, like a grid of buoys bobbing on the ocean.

The plan is to monitor a carefully-selected set of pulsars in an attempt to capture this effect.  Making the measurements with the required accuracy is not easy, but there are several radio-telescope arrays that are now, or will shortly be, coming on-stream.  These observatories should be able to make measurements of the requisite precision.  And, although the scientific potential of the experiment is large, the incremental cost (over and above that which would be spent on the radio telescopes anyway) is relatively modest.

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