Abstract:
12C is a node in the chemical evolution of the Universe. It was first formed in large abundance in primordial stars 400 million years after the Big Bang. Various production paths are possible due to the pronounced alpha cluster structure of light nuclei that facilitates the conversion of primordial elements into the Carbon Oxygen range. Of particular importance is the emerging ratio of 12C/16O which is determined by the subsequent 12C(a,g)16O reaction, which also is determined by the a cluster structure of 16O. Several examples will be presented how this rate influences the composition of white dwarfs and determines the size of the black hole gap generated by pair production supernovae. The 12C+12C fusion rate on the other hand determines the stellar evolution of massive stars towards the final fate as core collapse supernovae but also serves as ignition point for thermonuclear supernovae (SN Ia) in accreting or merging white stars and superbursts in the atmosphere of accreting neutron stars.