Gravitational waves squash and stretch space as they travel through the universe. Current attempts to spot them involve monitoring a region of space several kilometres across on Earth for the tell tale signs of this squeezing. Although great things are expcted, these experiments have so far thrown up precisely nothing.
But there’s another way. 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.
So the plan is to keep a beedy eye on an array of carefully chosen pulsars. It’s called the North American Nanohertz Observatory for Gravitational Waves or NANOGrav and it’s part of an international effort to spot gravitational waves in this way.
Of course, these kinds of observations are hard to make. First, astronomers need well-characterised millisecond pulsars to observe. They’re not easy to find and there appears to be a particular dearth of them in the northern hemisphere. And measuring them with the required accuracy isn’t easy either, say Fredrick Jenet at the University of Texas, Brownsville, and a few buddies.
But there’s hope on the horizon. These guys say the next generation of radio telescope arrays such as the Allen Telescope Array in California and the Square Kilometer Array in Australia or South Africa, should be capable of making the required measurements. And the scientific potential of the data is huge.
The team says the observations should help them understand how galaxies and supermassive black holes evolve together, shed light on the physics of the early universe such as inflation as well as probing the nature of space-time, perhaps revealing quantum gravity corrections to classical gravity. It may even throw up some new sources of gravitational waves.
Of course, many of those things are also the goals of the Earth-based gravitational wave observatories, which have cost hundreds of millions of dollars to build and more to maintain and upgrade. By contrast, the NANOGrav team estimates the cost of its project over ten years to be a mere $66 million.
It expects to be up and running by 2020 and at that price looks remarkably good value.
Ref: arxiv.org/abs/0909.1058: The North American Nanohertz Observatory for Gravitational Waves