Scientists Just Discovered How the Universe Builds Monster Black Holes

A new gravitational-wave study of 153 confident black hole mergers in GWTC4 finds two distinct black hole populations.

The heaviest black holes show spin and mass patterns consistent with second-generation mergers in dense star clusters.

The results support hierarchical growth through repeated mergers rather than direct stellar collapse.

The study also strengthens evidence for the predicted pair-instability mass gap, refining tests of stellar evolution and cluster dynamics.