The Milky Way Is a Gravitational Wave Detector
LIGO uses 4-kilometre laser arms to detect gravitational waves at hundreds of hertz. Pulsar timing arrays use millisecond pulsars scattered across the Milky Way — arms measured in light-years — to detect gravitational waves at nanohertz frequencies, ten orders of magnitude lower. In June 2023, five independent pulsar timing arrays simultaneously announced the detection of a stochastic gravitational wave background. The Milky Way itself was the detector.