Gravitational waves reveal the pair-instability mass gap and constrain nuclear burning in massive stars
Nature Astronomy Springer Nature
Authors:
Fabio Antonini, Isobel M Romero-Shaw, Thomas Callister, Fani Dosopoulou, Debatri Chattopadhyay, Barry Ginat, Mark Gieles, Michela Mapelli
Abstract:
Pair-instability should prevent the direct formation of black holes above about 50M⊙ creating a “pair-instability” mass gap. Yet gravitational-wave obser vations have detected black holes in this mass range. These systems can be explained with uncertainties in massive-star evolution, or hierarchical mergers in stellar clusters, which are expected to produce large spins with isotropic orien tations. Here we present evidence for the pair-instability mass gap in the LIGO–Virgo–KAGRA fourth transient catalog, with a lower edge at 44.3 +5.9 −3.5 M⊙. We also obtain a measurement of the 12C(α, γ) 35 16O reaction rate, yielding an Sfactor of 268+195 −116 keV b, a parameter critical for modeling helium burning and stellar evolution. The data reveal two populations: a low-spin group with no black holes above the gap, and a high-spin, isotropic group that extends across the full mass range and occupies the gap, consistent with hierarchical mergers. These findings are consistent with pair-instability playing a role in shaping the black hole mass spectrum, point to a connection between gravitational wave astronomy and nuclear astrophysics, and highlight dense stellar clusters as key environments in the growth of black holes.
