What fraction of merging black holes comes from each channel?
In plain words
Black-hole pairs could form from two stars born together, from encounters in crowded star clusters, or inside gas disks around supermassive black holes.
Precise statement
Determine the fractions of the LIGO-Virgo-KAGRA binary black hole population arising from isolated binary evolution (common envelope, stable mass transfer, chemically homogeneous evolution), dynamical assembly in globular, nuclear and young clusters, AGN disks and hierarchical mergers, using the distributions of masses, effective and precessing spins $(\chi_{\mathrm{eff}}, \chi_{p})$, mass ratio and redshift. Answer: fractions with credible intervals.
What would settle it
Population inference on a catalog of order $1e3$ events with spin and eccentricity measurements that separate channel signatures.
Status in the literature
Unverified note
2025: the GWTC-4.0 catalog added the events of the first part of the fourth observing run; the mass distribution shows structure (peaks near $10\ \text{and}\ 35\,M_{\mathrm{sun}}$) not yet assigned to channels.