The North American Nanohertz Observatory for Gravitational Waves, a collaboration using pulsar timing to detect gravitational waves.NANOGrav is a collaboration of astronomers and physicists that uses an array of precisely timed pulsars—rapidly spinning neutron stars—as cosmic clocks to detect gravitational waves. By measuring tiny variations in the arrival times of radio pulses from many pulsars, the collaboration can sense the stretching and squeezing of space-time caused by passing gravitational waves. In 2023, NANOGrav announced evidence for a gravitational wave background, likely originating from supermassive black hole mergers.
NANOGrav was founded in 2007 as a collaboration of US institutions, building on earlier pulsar timing efforts. It uses the Green Bank Telescope, Arecibo Observatory (until its collapse), and the Very Large Array.
Gravitational waves passing through Earth cause slight changes in the distance between Earth and each pulsar, altering the pulse arrival times. By monitoring dozens of pulsars over many years, NANOGrav looks for a correlated pattern of timing residuals across the sky—a signature of gravitational waves. The technique is analogous to using a galaxy-sized detector, with each pulsar acting as a 'tick' of a clock.
NANOGrav's primary application is detecting and studying gravitational waves at nanohertz frequencies, which are invisible to ground-based detectors like LIGO. This opens a new window into supermassive black hole mergers and the early universe.
The pulsars used by NANOGrav are so stable that they rival atomic clocks, with some showing timing precision better than a microsecond over decades.



















