Astronomers Detect Gravitational Waves from Black Hole Mergers

On June 28, 2023, multiple international pulsar timing array consortia — NANOGrav in North America, EPTA in Europe, PPTA in Australia, CPTA in China, and the IPTA — announced coordinated evidence of a nanohertz gravitational wave background pervading the universe. Each used 15-25 years of radio observations of millisecond pulsars to detect low-frequency spacetime distortions, attributed by current models to inspiraling supermassive black hole binaries throughout cosmic history. The detection opens a new observational window on the universe at frequencies billions of times lower than those measured by ground-based detectors like LIGO.