The 12C+12C fusion reactions at astrophysical energies

The fusion reactions 12C(12C,α)20Ne and 12C(12C,p)23Na are referred to as carbon burning in stars. In massive stars the ashes produced during helium burning become the fuel for further nuclear-burning processes, leading to the synthesis of most elements with mass numbers larger than 20. Consequently, these fusion reactions represent key processes since they influence not only the nucleosynthesis but also the subsequent evolution of a star. However, at the astrophysical relevant energies the reaction rate of these fusion reactions is not very well known and provided only by extrapolations of high energy data. The reactions have now been studied from E=1.5 to 4.75 MeV by γ-ray and particle spectroscopy using thick carbon targets. The data reveal new resonances, in particular strong resonances at E<2.3 MeV, which lie in the range of the Gamow peak for carbon burning in massive stars, which takes place at temperatures T∼(5-10) x 108 K. These resonances increase the present reaction rate significantly in this temperature range. The impact of the results on various astrophysical sites, e.g. supernovae progenitor stars, is discussed.