Stellar Nucleosynthesis

Stellar nucleosynthesis refers to the assembly of the natural abundances of the chemical elements by nuclear reactions occurring in the cores of stars. Those stars evolve (age) owing to the associated changes in the abundances of the elements within. Those stars lose most of their mass when it is ejected late in the stellar lifetimes, thereby enriching the interstellar gas in the abundances of elements heavier than helium. For the creation of elements during the explosion of a star, the term supernova nucleosynthesis is used. The goal is to understand the vastly differing abundances of the chemical elements and their several isotopes as a process of natural history. The primary stimulus to the development of this theory was the shape of the natural abundances. Those abundances, when plotted on a graph as a function of atomic number of the element, have a jagged sawtooth structure varying by factors of ten million. This suggested a natural process rather than a random distribution. Such a graph of the abundances can be seen at History of nucleosynthesis theory. Stellar nucleosynthesis is the most dominating contributor to several processes that also occur under the collective term nucleosynthesis.

A second major stimulus to understanding the processes involved occurred throughout the 20th century, when it was first realized that the energy released from nuclear fusion reactions accounted for the longevity of the Sun as a source of heat and light. The fusion of heavier nuclei from initial hydrogen and helium provides that energy source, which synthesizes new nuclei as a byproduct of the fusion. This became clear during the decade prior to WWII. Those associated fusion product nuclei are restricted to nuclei only slightly heavier than the fusing nuclei, however, and thus do not contribute heavily to the natural abundances of the elements. Nonetheless, this success raised the plausibility of explaining all of the natural abundances in this way. The prime energy producer in the sun is the fusion of hydrogen to helium, which occurs at a minimum temperature of 3 million kelvin.