What 267 black hole mergers reveal about how they form

Analyzing all 267 gravitational-wave detections through GWTC-5.0, LIGO-Virgo-KAGRA maps the black hole merger rate at 27–49 per cubic gigaparsec per year and uncovers a distinct subpopulation with high spins (χ~0.7) at two mass scales — strong evidence that some black holes grew by swallowing earlier merger remnants. The data also show that black holes near 35 solar masses preferentially pair with similar-mass partners, while heavier ones increasingly merge with unequal companions, tracing out the fingerprints of different stellar-environment formation channels.