Extending the Hoyle-State Paradigm to C 12 + C 12 Fusion

Carbon burning is a key step in the evolution of massive stars, Type 1a supernovae and superbursts in x-ray binary systems. Determining the C12+C12 fusion cross section at relevant energies by extrapolation of direct measurements is challenging due to resonances at and below the Coulomb barrier. A study of the Mg24(α,α′)Mg24 reaction has identified several 0+ states in Mg24, close to the C12+C12 threshold, which predominantly decay to Ne20(ground state)+α. These states were not observed in Ne20(α,α0)Ne20 resonance scattering suggesting that they may have a dominant C12+C12 cluster structure. Given the very low angular momentum associated with sub-barrier fusion, these states may play a decisive role in C12+C12 fusion in analogy to the Hoyle state in helium burning. We present estimates of updated C12+C12 fusion reaction rates.