Two independent teams analyzed gravitational-wave data from ~hundreds of black hole mergers (LIGO/Virgo/KAGRA catalog) and both identified a distinct subpopulation of unusually massive black holes (≥40 solar masses) with high, randomly-oriented spins. Plunkett's MIT team interprets this spin signature as evidence these are "second-generation" mergers—black holes formed from earlier mergers rather than stellar collapse. Banagiri's Monash team reached similar mass thresholds and found high spins but noted the origin interpretation should be treated cautiously. The practical claim: gravitational-wave signals encode subtle mass and spin fingerprints that can distinguish formation pathways (binary stellar pairs vs. dynamical encounters vs. hierarchical mergers), potentially explaining how some black holes reach otherwise-implausible mass ranges and seeding models for supermassive black hole growth. The source doesn't specify exact sample sizes, statistical confidence bounds, or how the two teams' methods differ substantively—only that one assumes spin alignment structure and the other is "data-driven."