Author(s): Cailin Plunkett, Salvatore Vitale, Thomas Callister, and Michael Zevin (Society of Physicists Interested in Non-Aligned Spins (SPINS)) Different analyses of gravitational-wave observations are converging on evidence for a distinct population of massive black hole binaries produced through repeated mergers. [Phys. Rev. Lett. 137, 021404] Published Mon Jul 06, 2026