The advanced evolution of massive stars: I. New reaction rates for carbon and oxygen nuclear reactions

TL;DR

This study demonstrates that revised nuclear reaction rates for key carbon and oxygen channels markedly affect the late-stage evolution of massive stars, including burning lifetimes, core structure, and s-process nucleosynthesis. By comparing CF88, Hindrance (HIN(RES)), and TDHF-derived rates within the GENEC framework, the authors show that the $^{12}$C$(\alpha,\gamma)^{16}$O rate shifts the $^{12}$C/$^{16}$O balance and modestly alters the CO core mass, while fusion-rate choices for $^{12}$C+$^{12}$C and $^{16}$O+$^{16}$O mainly modulate burning durations, ignition conditions, and shell convection, thereby influencing core compactness and remnant fate. TDHF tends to prolong C-burning and reduce ignition temperatures, whereas the Hindrance model reduces fusion rates and shortens subsequent burning phases, with observable consequences for surface abundances and inner-core composition. The work also refines s-process predictions via updated neutron-source rates and a high-resolution one-zone nucleosynthesis treatment, though overall changes remain modest due to the short advanced-burning durations. The findings underscore how uncertainties and advances in nuclear reaction rates propagate through stellar structure, nucleosynthesis, and remnant outcomes, underscoring the need for integrated experimental and theoretical efforts, including rotation and magnetic effects, to improve predictive power for supernova ejecta and compact remnants.

Abstract

The nuclear rates for reactions involving 12C and 16O are key to compute the energy release and nucleosynthesis of massive stars during their evolution. These rates shape the stellar structure and evolution, and impact the nature of the final compact remnant. We explore the impact of new nuclear reaction rates for 12C(α,γ)16O, 12C+12C, 12C+16O and 16O+16O reactions for massive stars. We aim to investigate how the structure and nucleosynthesis evolve and how these processes influence the stellar fate. We computed stellar models using the GENEC code, including updated rates for 12C(α,γ)16O and, for the three fusion reactions, new rates following a fusion suppression scenario and new theoretical rates obtained with TDHF calculations. The updated 12C(α,γ)16O rates mainly impact the chemical structure evolution changing the 12C/16O ratio with little effect on the CO core mass. This variation in the 12C/16O ratio is critical for predicting the stellar fate, which is very sensitive to 12C abundance. The combined new rates for 12C+12C and 16O+16O fusion reactions according to the HIN(RES) model lead to shorter C- and O-burning lifetimes, and shift the ignition conditions to higher temperatures and densities. Theoretical TDHF rates primarily affect C-burning, increasing its duration and lowering the ignition temperature. These changes alter the core chemical structure, the carbon shell size and duration, and hence the compactness. They also affect nucleosynthesis. This work shows that accurate reaction rates for key processes in massive star evolution drive significant changes in stellar burning lifetimes, chemical evolution, and stellar fate. In addition, discrepancies between experimental and theoretical rates introduce uncertainties in model predictions, influencing both the internal structure and the supernova ejecta composition.

Figures (13)

• Figure 1: Reaction rates for the four main nuclear reactions involving $^{12}$C and $^{16}$O. Top left: Rates from deBoer2017 normalised to Kunz2002 reference for the $\rm ^{12}C(\alpha,\gamma)^{16}O$ reaction. The grey hatched areas indicate the temperature ranges where core and shell He-burning occur in the GENEC rotating model explored mass range. For the rest of the panels, nuclear reaction rates are taken from CF88 (black), HIN(RES (blue), and TDHF (magenta), all normalised to the CF88 rates ($N_A <\sigma v>_{CF88}$). Shaded areas (with corresponding colour codes) indicate the temperature ranges where core and shell C-burning and core O-burning take place in the 15 and 17 $M_{\odot}$ GENEC rotating models.
• Figure 2: Evolution of central temperature ($\rm T_C$) vs. central density ($\rm \rho_C$) for rotating models of 15 M$_{\odot}$ at solar metallicity, shown for the three nuclear reaction rate references considered in this work along with the full Hindrance scenario (HIN model) with each model colour-coded accordingly. Nuclear ignition points are marked by crosses. Models from D24 are indicated in dashed-lines for the CF88, HIN, and HIN(RES) models. The dash-dotted grey line indicates the boundary for degenerate conditions inside the core, while the shaded grey area denotes the domain affected by electron-positron pair instability.
• Figure 3: Energy production rates $\epsilon$ [erg.$\rm g^{-1}$.$\rm s^{-1}$] inside a 15 M$_{\odot}$ rotating star for varying reaction rates. Left: Energy during shell C-burning, approximatively 3000 years after core C-ignition. Right: Energy during core O-burning at central $X_{^{16}O} = 0.3$. The pale areas in orange indicate where the gravitational energy is negative, i.e. corresponding to an expansion.
• Figure 4: Mass fraction of central abundances for a rotating 15 $M_{\odot}$ from He-burning to O-burning, shown for the three nuclear models: CF88, HIN(RES), and TDHF (line-coded). For comparison, a CF88 model using the rates from Kunz2002 is shown in dotted lines. Shaded areas show the successive nuclear burning phases with colours corresponding to He-, C-, Ne-, and O-burning (grey, red, green, and blue, respectively).
• Figure 5: Profiles of abundances of $^4$He, $^{12}$C, $^{16}$O, $^{20}$Ne, $^{23}$Na, $^{28}$Si, $^{32}$S, $^{34}$S, and $^{44}$Ti (colour-coded) for a rotating 15 M$_{\odot}$, shown for different reaction rates scenarios distinguished by line style. Left panel: End of the C-burning phase. Right panel: End of the O-burning phase.