Nucleosynthesis Processes in Stellar Evolution

Nucleosynthesis encompasses the network of nuclear reactions that forge the elements within stars and during stellar death. In the cores of main-sequence stars, hydrogen burning via the proton–proton chain and the CNO cycle builds helium under hydrostatic conditions. As stars evolve, successive burning stages (helium, carbon, neon, oxygen and silicon burning) synthesise elements up to iron. Beyond iron, energy constraints inhibit further fusion, so heavier nuclei arise through neutron-capture reactions. The slow neutron-capture process (s-process) in asymptotic giant branch (AGB) stars adds neutrons more slowly than nuclei decay, producing many of the elements from strontium to lead. The rapid neutron-capture process (r-process) operates where extreme neutron fluxes permit successive captures faster than β-decay, typically in explosive environments such as neutron star mergers or certain supernovae, yielding the heaviest elements including gold and uranium. A third channel, the p-process, generates proton-rich isotopes via photodisintegration in supernova shock fronts. Observations of isotopic signatures in presolar grains, combined with stellar models and galactic chemical evolution studies, link these processes to the chemical enrichment of galaxies. Chronometers based on short-lived radioisotopes constrain the timescales of star formation and solar system assembly, while spectroscopic surveys trace neutron-capture element abundances across galactic populations. Together, these approaches reveal how stellar mass, metallicity and explosion physics interconnect to shape the cosmic origin of the elements and inform models of chemical evolution, star-planet formation and nucleosynthesis chronometry.

Research from Nature Portfolio

Recent studies have achieved the first direct measurement of bound-state β-decay of fully ionised 205Tl, a decay mode active only in highly charged ions. The new half-life determination, nearly five times longer than prior theoretical estimates and with 10 per cent uncertainty, removes a major barrier to accurate predictions of 205Pb production in AGB stars. Incorporating the revised decay rates into stellar models has yielded more precise 205Pb abundances, which, when coupled with galactic chemical evolution calculations and meteoritic isotope ratios, constrain the isolation interval of solar material within its birth molecular cloud. This advance refines the s-process chronometer based on the 205Pb–205Tl system and strengthens our understanding of both AGB nucleosynthesis and early solar system chronology.

Nucleosynthesis Processes in Stellar Evolution publication trend

The graph below shows the total number of articles in nucleosynthesis processes in stellar evolution across all publications each year (not limited to Nature Index journals).

Technical terms

Nucleosynthesis: The network of nuclear reactions responsible for creating new atomic nuclei in stars and explosive astrophysical events.

Slow neutron-capture process (s-process): A nucleosynthesis pathway in which seed nuclei capture neutrons at rates slower than β-decay, predominantly in AGB stars, producing elements up to lead and bismuth.

Rapid neutron-capture process (r-process): A sequence of neutron captures occurring faster than β-decay, requiring high neutron fluxes in environments such as neutron star mergers or particular supernovae, forming the heaviest elements.

Presolar grains: Microscopic mineral inclusions in meteorites that formed before the Solar System and retain isotopic fingerprints of their stellar origins.

Bound-state β-decay: A decay mode in which an entirely ionised nucleus captures and decays a bound-state electron, influencing isotope half-lives under stellar conditions.

Neutron-capture cross section: A measure of the probability that a nucleus will absorb a neutron, critical for modelling nucleosynthesis pathways and elemental yields.

References

1. High-temperature 205Tl decay clarifies 205Pb dating in early Solar System. Nature (2024).
2. New Constraints for Supernova Models from Presolar Silicon Carbide X Grains with Very High 26Al/27Al Ratios. The Astrophysical Journal Letters (2023).
3. Measurement of the Ce140(n,γ) Cross Section at n_TOF and Its Astrophysical Implications for the Chemical Evolution of the Universe. Physical Review Letters (2024).
4. Presolar Grains as Probes of Supernova Nucleosynthesis. Space Science Reviews (2024).
5. Observational constraints on the origin of the elements – VI. Origin and evolution of neutron-capture elements as probed by the Gaia-ESO survey. Monthly Notices of the Royal Astronomical Society (2023).
6. The Origin of Elements from Carbon to Uranium. The Astrophysical Journal (2020).