The advanced evolution of massive stars

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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.
Funding Information
  • ChETEC (101008324)

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