The advanced evolution of massive stars

I. New reaction rates for carbon and oxygen nuclear reactions

¹ University of Strasbourg, CNRS, IPHC UMR 7178, postcodeF-67000 Strasbourg, France
² Departament d’Astonomia i Astrofísica, Universitat de València, C/Dr. Moliner, 50, E-46100 Burjassot (València), Spain
³ Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium
⁴ Observatori Astronòmic, Universitat de València, 46980 Paterna, Spain
⁵ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁶ Facility for Rare Isotope Beams, Michigan State University, East Lansing, Michigan 48824, USA
⁷ Department of Fundamental and Theoretical Physics, and Department of Nuclear Physics and Accelerator Applications, Research School of Physics, Australian National University, Canberra ACT 2600, Australia
⁸ Laboratoire des 2 Infinis – Toulouse (L2IT-IN2P3), Université de Toulouse, CNRS, UPS, F-31062 Toulouse Cedex 9, France
⁹ University of Strasbourg, Institute of Advanced Studies (USIAS), Strasbourg, France

^⋆ Corresponding author: thibaut.dumont@iphc.cnrs.fr

Received: 28 April 2025
Accepted: 5 August 2025

Abstract

Context. The nuclear rates for reactions involving ¹²C and ¹⁶O are key to computing the energy release and nucleosynthesis evolution of massive stars during their advanced burning phases. Ultimately, these burning rates shape the stellar structure and evolution and influence the nature of the compact objects produced at the end of the stellar life.

Aims. We explore the implications of new nuclear reaction rates from both experimental and theoretical studies for ¹²C(α, γ)¹⁶​O, ¹²C+¹²​C, ¹²C+¹⁶​O, and ¹⁶O+¹⁶​O reactions for massive stars. Our goal is to investigate how the chemical structure and nucleosynthesis evolve from the He-exhaustion stage to the O-burning phase and how these processes influence the ultimate stellar fate.

Methods. We computed rotating and non-rotating models for stars of different masses at solar metallicity. We used the stellar evolution code GENEC, which includes a large network of nuclear reactions and isotopes involved in advanced phases, as well as updated rates for ¹²C(α,γ)¹⁶O. For the three fusion reactions involving ¹²C and ¹⁶O, we considered new rates following a data-driven fusion suppression scenario (hereafter HIN(RES)) and new theoretical rates obtained with time-dependent Hartree-Fock (TDHF) calculations.

Results. The updated ¹²C(α, γ)¹⁶​O rates mainly impact the chemical structure evolution changing the ¹²C/¹⁶O ratio at He-exhaustion and have little effect on the CO core mass. This variation in the ¹²C/¹⁶O ratio is in some cases critical for predicting the final fate of the model, which is very sensitive to ¹²C abundance, and in particular the 20 M_⊙ remnant may change from a black hole to a neutron star. The He-burning (C-burning) lifetime is also decreased (increased) by about −2% (+15%). The combined new rates for ¹²C+¹²​C and ¹⁶O+¹⁶​O fusion reactions according to the HIN(RES) model lead to shorter C- and O-burning lifetimes by ≈ − 10%, and −50%, respectively, and shift the ignition conditions to higher temperatures and densities. In contrast, the theoretical TDHF rates primarily affect C-burning, increasing its duration by about 30% and lowering the ignition temperature. These changes modify the chemical structure of the core, the size and duration of C-burning shells, and hence their compactness. They also impact the central and shell nucleosynthesis (by ±1 dex and by factors of ±2–10, respectively), while ¹²C+¹⁶​O reaction rates variations remain the least important.

Conclusions. The present work shows that accurate reaction rates for key processes in massive star evolution and nucleosynthesis drive significant changes in stellar burning lifetimes, chemical evolution, and stellar fate. The multiple and cumulative consequences of these changes are significant and should not be neglected. In addition, discrepancies between experimental and theoretical rates introduce uncertainties in model predictions, influencing both the internal structure and the composition of the supernova ejecta.