NANOGrav (North American Nanohertz Observatory for Gravitational Waves) is a Pulsar Timing Array, incorporating Arecibo Observatory and the Green Bank Telescope of the National Radio Astronomy Observatory. It is an effort to detect Gravitational Waves through comparison of the timing of observed Pulsar cycles.
Gravitational Wave (GW)
International Pulsar Timing Array (IPTA)
Nanohertz Gravitational Waves
Pulsar Timing Array (PTA)