Suppose you’re an astronomer trying to detect fiendishly subtle ripples in space-time sent from objects made of exotic matter. How would you do it?
How about with a GPS system? That’s the idea behind NANOGrav, the North American Nanohertz Observatory for Gravitational Waves.
NANOGrav acts as a kind of GPS, but rather than a fleet of global positioning satellites orbiting Earth, the project uses an array of 54 pulsars orbiting the galaxy. And instead of locating your position on Earth, NANOGrav uses the pulsar radio signals to look for tiny shifts in the position of our planet in space.
“Imagine a sphere containing these pulsars being squeezed and stretched by gravitational waves,” says UWM physics professor Xavier Siemens. As gravitational waves disturb the space-time in this sphere, which spans hundreds of light-years, NANOGrav should detect tiny variations in the signals from the pulsars.
“That’s one of the beautiful parts of this experiment,” says Siemens, the principal investigator on a $14.5 million, five-year grant to establish and operate the NANOGrav Physics Frontiers Center. “Nature has built an important part of the apparatus for us, and we get that for free.”
Although the successful LIGO project provides one method of finding gravitational waves, NANOGrav lets scientists study gravitational wave frequencies inaccessible with other discovery methods. By observing low-frequency gravitational waves, NANOGrav could provide information on phenomenon like super-massive black hole binaries or gravitational wave echoes from the earliest stages of the universe.
NANOGrav is sifting through radio waves collected by the gigantic Arecibo Observatory in Puerto Rico and the Robert C. Byrd Green Bank Telescope in West Virginia, looking for signs of these fantastically huge gravitational waves.
As with LIGO, the NANOGrav scientists hope to discover something that could disrupt conventional physics wisdom, such as cosmic strings. Although considered outlandish by some scientists, they are a theoretical artifact from the universe’s rapid expansion during an infinitesimal moment after the Big Bang.