부산대학교 도서관

Carbon burning powers scenarios that influence the fate of stars, such as the late evolutionary stages of massive stars1(exceeding eight solar masses) and superbursts from accreting neutron stars2,3. It proceeds through the 12C + 12C fusion reactions that produce an alpha particle and neon-20 or a proton and sodium-23—that is, 12C(12C, α)20Ne and 12C(12C, p)23Na—at temperatures greater than 0.4 × 109kelvin, corresponding to astrophysical energies exceeding a megaelectronvolt, at which such nuclear reactions are more likely to occur in stars. The cross-sections4for those carbon fusion reactions (probabilities that are required to calculate the rate of the reactions) have hitherto not been measured at the Gamow peaks4below 2 megaelectronvolts because of exponential suppression arising from the Coulomb barrier. The reference rate5at temperatures below 1.2 × 109kelvin relies on extrapolations that ignore the effects of possible low-lying resonances. Here we report the measurement of the 12C(12C, α0,1)20Ne and 12C(12C, p0,1)23Na reaction rates (where the subscripts 0 and 1 stand for the ground and first excited states of 20Ne and 23Na, respectively) at centre-of-mass energies from 2.7 to 0.8 megaelectronvolts using the Trojan Horse method6,7and the deuteron in 14N. The cross-sections deduced exhibit several resonances that are responsible for very large increases of the reaction rate at relevant temperatures. In particular, around 5 × 108kelvin, the reaction rate is boosted to more than 25 times larger than the reference value5. This finding may have implications such as lowering the temperatures and densities8required for the ignition of carbon burning in massive stars and decreasing the superburst ignition depth in accreting neutron stars to reconcile observations with theoretical models3. The rate of carbon burning—12C + 12C fusion—in stars is boosted by resonant behaviour at astrophysical energies.