Nuclear clusters as first stepping-stones towards the chemical evolution of our Universe

Michael Wiescher (University of Notre Dame, USA)

Nuclear reactions in stars have facilitated the chemical evolution of the universe from the Big Bang to present times. This evolution can be mapped by the spectroscopic observation of old to present stars and the present level is reflected in the radioactive glow of the Milky Way. However, there are still fundamental questions about the first step in this development, the conversion of the primordial hydrogen, helium and lithium abundances into the carbon, nitrogen and oxygen that characterize the abundance distributions in oldest stars observed so far. This step took place in the first generation of stars that also ended the dark age of the universe some 300 million years after the Big Bang. This step requires nuclear reaction processes that bridge the mass 5 and mass 8 gaps of instability. The key is in the existence of nuclear cluster configurations in light nuclei that serve as stepping stones for α induced reaction processes helping to bridge the gap. I will summarize the various processes that are presently being discussed and describe the experimental evidence that support this interpretation.