Hubble Constant Puzzle Deepens as Supernova and CMB Measurements Clash

Astronomers are testing a new way to measure the universe’s expansion rate using the gravitational-wave background detected by NANOGrav. By treating the cosmic hum from merging supermassive black holes as a statistical “stochastic siren,” researchers hope to calculate the Hubble constant and help resolve the long-standing Hubble tension between supernova and cos...