How Gravitational Waves Could Generate Radio Signals

Any time now, the folks at the gravitational wave detector LIGO expect to come across conclusive evidence that their search is over. If the theorists have their numbers right, the machine should spot a passing gravitational wave sometime in the next year or so.

LIGO works by watching for the tell-tale squeezing and stretching of space as gravitational waves pass by. But might there be another way to spot these waves?

For some 40 years now, various physicists have pointed out that gravity waves ought to produce electromagnetic waves. Today, Peter Hogan and Shane O’Farrell at University College Dublin in Ireland resurrect the idea.

The mechanism is straightforward. Create a uniform magnetic field of the same scale as a gravitational wave and place it in the path of an incoming wave. The subsequent squeezing and shaking of this magnetic field should then generate electromagnetic radiation, just as any other kind of shaking would.

The trouble is that gravitational waves have a tiny amplitude and a relatively low frequency meaning that the resultant radio waves would be mind-bogglingly weak. (Obviously, higher frequency g-waves will produce higher frequency em waves.)

Would they be harder to detect than a change in length of less than the diameter of proton, as LIGO measures?

That’s hard to say. Those calculations simply haven’t been done yet. But it’ll be interesting see what numbers they produce.

About 1 per cent of the noise you see on the screen of a badly-tuned analogue TV is the cosmic background radiation–the echo of the Big Bang. Wouldn’t it be cool to know that your old Sony Trinitron could also tune into the sound of black holes colliding.

Ref: arxiv.org/abs/0905.2834: Generating Electromagnetic Waves from Gravity Waves in Cosmology