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

Abstract

Carbon burning is a key step in the evolution of massive stars, Type 1a supernovae and superbursts in x-ray binary systems. Determining the 12C þ 12C 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 24Mgðα; α0Þ24Mg reaction has identified several 0þ states in 24Mg, close to the 12C þ 12C threshold, which predominantly decay to 20Neðground stateÞ þ α. These states were not observed in 20Neðα; α0 Þ20Ne resonance scattering suggesting that they may have a dominant 12C þ 12C cluster structure. Given the very low angular momentum associated with sub-barrier fusion, these states may play a decisive role in 12C þ 12C fusion in analogy to the Hoyle state in helium burning. We present estimates of updated 12C þ 12C fusion reaction rates.