New analysis of gravitational wave data indicates that the universe's heaviest black holes arise from multiple collisions inside dense star clusters instead of single stellar collapses.
Researchers at Cardiff University examined 153 black hole mergers recorded in version 4.0 of the LIGO-Virgo-KAGRA Gravitational-Wave Transient Catalog. Their study, published in Nature Astronomy, identifies two separate populations of black holes. Lower-mass objects match expectations for direct formation from dying stars, while higher-mass ones show rapid spins in random orientations consistent with repeated mergers in crowded environments where stars are packed far more densely than near the Sun.