In 2015, when scientists, for the first time ever, directly detected gravitational waves—ripples in spacetime—from colliding black holes, the result came as a shock to some astronomers. Based on previous studies of black holes using x-rays, many experts expected that each member of a merging pair would typically weigh about 10 times the sun’s mass, but the 2015 merger featured twin giants three times that heavy. And the Laser Interferometer Gravitational-wave Observatory (LIGO), which enabled the discovery, has been spotting bizarrely big pairs ever since.