Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso

P-P Chains

  • Nikos PrantzosEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_1261-4


The p-p chain is the series of nuclear reactions converting four protons to one 4He nucleus and releasing an energy of about 6.6 MeV/nucleon or 5 × 1018 erg/gr. This provides the main source of energy for Main sequence stars of less than 1.3 M. while in more massive stars the CNO cycle dominates. The first reaction of the series (p + p → D + e+ + νe + 0.42 MeV) involves a slow, weak interaction (the conversion of a proton into a neutron), which is responsible for the long lifetimes (>10 Gyr) of the Sun and other low mass stars.

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© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Institut d’Astrophysique de ParisParisFrance