Measurement prospects for the pair-instability mass cutoff with gravitational waves

Pair-instability supernovae leave behind no compact remnants, resulting in a predicted gap in the distribution of stellar black-hole masses. Gravitational waves from binary black-hole mergers probe the relevant mass range and analyses of the LIGO–Virgo–KAGRA catalog (GWTC-4) indicate a possible mass cutoff at 40 − 50 M ⊙ . However, the robustness of this result remains unclear. To this end, using full Bayesian parameter estimation, we simulate gravitational-wave catalogs with and without such a mass cutoff and then test whether its presence or absence is correctly inferred with parametric population models. For catalogs similar to GWTC-4, confident identification of a cutoff is not guaranteed, but the best constraints among our simulations are compatible with results from GWTC-4 when the model includes a cutoff. Conversely, spurious identification of a cutoff is unlikely. For catalogs expected by the end of the O4 observing run, uncertainty in the cutoff mass is reduced by ≳ 20 % , but a cutoff at 40 − 50 M ⊙ yields only a lower bound on the C 12 ( α , γ ) 16 O reaction rate, our most stringent constraints on the S factor at 300 keV being S 300 ≳ 125 keV b at 90% credibility. Relative uncertainties on the Hubble parameter H 0 from gravitational-wave data alone can still be up to 100%. We also analyze GWTC-4 with the nonparametric population model, finding that some mass features are more prominent than in parametric models but a sharp cutoff is not required. However, the parametric model passes a likelihood-based predictive test in GWTC-4 and the results are consistent with those from our simulated catalogs with a cutoff. Such tests are necessary to make astrophysical claims from gravitational-wave catalogs.