As gravitational waves sweep past a pulsar at the speed of light, the waves will very slightly expand and contract the distance between the pulsar and the Earth, ever so slightly changing the time between the ticks. The NANOGrav team used pulsars that rotate incredibly fast – up to 1,000 times per second – and these pulses can be timed like the ticking of an extremely accurate cosmic clock. Pulsars are functionally similar to a lighthouse – as they spin, their beams can sweep across the Earth at regular intervals.
The team used pulsars, rapidly spinning dead stars that emit a beam of radio emissions. The NANOGrav collaboration is also trying to detect spacetime ripples, but on an interstellar scale.
Researchers first detected direct evidence of gravitational waves in 2015, when the Laser Interferometer Gravitational-Wave Observatory, known as LIGO, picked up a signal from a pair of merging black holes that had traveled 1.3 billion light-years to reach Earth.
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