off energy in the process known as stellar nucleosynthesis. Nuclear fusion reactions create many of the lighter elements, up to and including iron and nickel Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang through nuclear reactions in a process called Big Bang nucleosynthesis. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions a There are several astrophysical processes which are believed to be responsible for nucleosynthesis. The majority of these occur within stars, and the chain of those nuclear fusion processes are known as hydrogen burning (via the proton–proton chain or the CNO cycle), helium burning, carbon burning, neon burning, oxygen burning and silicon burning. These processes are capable of creating elements up to and including iron and nickel. This is the region of nucleosynthesis within which the isotopes with the highest binding energy per nucleon are created. Heavier elements can be assembled within stars mainly by the slow neutron capture process known as the s-process or in explosive environments, such as supernovae and neutron star mergers, by the r-process, which involves rapid neutron captures (faster than the half-lifes of the intermediate isotopes). There is also a minor contribution from processes involving proton capture, such as the rp-process, and the p-process. These processes allow the synthesis of some proton-rich isotopes that cannot be created by neutron capture and subsequent beta-decays.