New Determination of the ¹²C(α, γ)¹⁶O Reaction Rate and Its Impact on the Black-hole Mass Gap

Abstract We present a precise measurement of the asymptotic normalization coefficient (ANC) for the 16 O ground state (GS) through the 12 C( 11 B, 7 Li) 16 O transfer reaction using the Quadrupole‐3‐Dipole (Q3D) magnetic spectrograph. The present work sheds light on the existing discrepancy of more than 2 orders of magnitude between the previously reported GS ANC values. This ANC is believed to have a strong effect on the 12 C( α , γ ) 16 O reaction rate by constraining the external capture to the 16 O ground state, which can interfere with the high-energy tail of the 2 + subthreshold state. Based on the new ANC, we determine the astrophysical S -factor and the stellar rate of the 12 C( α , γ ) 16 O reaction. An increase of up to 21% in the total reaction rate is found within the temperature range of astrophysical relevance compared with the previous recommendation of a recent review. Finally, we evaluate the impact of our new rate on the pair-instability mass gap for black holes (BH) by evolving massive helium core stars using the MESA stellar evolution code. The updated 12 C( α , γ ) 16 O reaction rate decreases the lower and upper edges of the BH gap about 12% and 5%, respectively.