Study Quantifies Uncertainties in Upper Edge of Pair-Instability Black Hole Mass Gap

A recent simulation study has evaluated how variations in stellar-evolution inputs affect the upper limit of the pair-instability supernova (PISN) black-hole mass gap. By altering nuclear reaction rates, mixing prescriptions and wind mass-loss in a suite of models, the researchers identified the 12C(α,γ)16O reaction as the primary source of uncertainty, capable of shifting the upper edge by roughly 30 solar masses. The triple-α reaction also produces a sizable shift of about 25 solar masses, while 16O+16O fusion can modify the upper edge by around 15 solar masses without influencing the lower edge, potentially widening or narrowing the gap.

Other factors, including additional nuclear processes and model details, affect the boundary by less than 10 solar masses. The study further reports that, unlike the lower edge, the upper edge remains stable across different spatial and temporal resolutions, suggesting current simulations reliably resolve it.

"The upper edge carries substantial theoretical uncertainty but is less prone to astrophysical contamination than the lower edge," the authors noted, emphasizing its value as a direct probe of the nuclear physics governing pair instability.

These results have implications for interpreting high-mass black-hole detections in gravitational-wave observations, helping to distinguish black holes formed through conventional stellar collapse from those arising via alternative channels.