The rate of the triple-α reaction that forms 12C affects1,2 the synthesis of heavy elements in the Ga–Cd range in proton-rich neutrino-driven outflows of core-collapse supernovae3,4,5. Initially, these outflows contain only protons and neutrons; these later combine to form α particles, then 12C nuclei via the triple-α reaction, and eventually heavier nuclei as the material expands and cools. Previous experimental work6,7 demonstrated that despite the high temperatures encountered in these environments, the reaction is dominated by the well characterized Hoyle state resonance in 12C nuclei. At sufficiently high nucleon densities, however, proton- and neutron-scattering processes may alter the effective width of the Hoyle state8,9. This raises the questions of what the reaction rate in supernova outflows is, and how changes affect nucleosynthesis predictions. Here we report that in proton-rich core-collapse supernova outflows, these hitherto neglected processes enhance the triple-α reaction rate by up to an order of magnitude. The larger reaction rate suppresses the production of heavy proton-rich isotopes that are formed by the νp process3,4,5 (where ν is the neutrino and p is the proton) in the innermost ejected material of supernovae10,11,12,13. Previous work on the rate enhancement mechanism9 did not anticipate the importance of this enhancement for proton-rich nucleosynthesis. Because the in-medium contribution to the triple-α reaction rate must be present at high densities, this effect needs to be included in supernova nucleosynthesis models. This enhancement also differs from earlier sensitivity studies that explored variations of the unenhanced rate by a constant factor1,2, because the enhancement depends on the evolving thermodynamic conditions. The resulting suppression of heavy-element nucleosynthesis for realistic conditions casts doubt on the νp process being the explanation for the anomalously high abundances of 92,94Mo and 96,98Ru isotopes in the Solar System1,3,14 and for the signatures of early Universe element synthesis in the Ga–Cd range found in the spectra of ancient metal-poor stars15,16,17,18,19,20.
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The simulation data that support these findings is available from the corresponding author upon reasonable request.
The reaction network library SkyNet used for this work is publicly available at https://bitbucket.org/jlippuner/skynet. The code used to run and analyse the simulations described here (which relies on the SkyNet library) is publicly available at https://bitbucket.org/lroberts/triplealphainmediumenhancement.
Wanajo, S., Janka, H.-T. & Kubono, S. Uncertainties in the νp-process: supernova dynamics versus nuclear physics. Astrophys. J. 729, 46 (2011).
Nishimura, N. et al. Uncertainties in νp-process nucleosynthesis from Monte Carlo variation of reaction rates. Mon. Not. R. Astron. Soc. 489, 1379–1396 (2019).
Fröhlich, C. et al. Neutrino-induced nucleosynthesis of A > 64 nuclei: the νp process. Phys. Rev. Lett. 96, 142502 (2006).
Pruet, J., Hoffman, R. D., Woosley, S. E., Janka, H. T. & Buras, R. Nucleosynthesis in early supernova winds. II. The role of neutrinos. Astrophys. J. 644, 1028–1039 (2006).
Wanajo, S. The rp-process in neutrino-driven winds. Astrophys. J. 647, 1323–1340 (2006).
Fynbo, H. O. U. et al. Revised rates for the stellar triple-α process from measurement of 12C nuclear resonances. Nature 433, 136–139 (2005).
Freer, M. & Fynbo, H. O. U. The Hoyle state in 12C. Prog. Part. Nucl. Phys. 78, 1–23 (2014).
Truran, J. W. & Kozlovsky, B. Z. The enhancement of the 3 4He → 12C reaction rate in dense matter by inelastic-scattering processes. Astrophys. J. 158, 1021–1032 (1969).
Beard, M., Austin, S. M. & Cyburt, R. Enhancement of the triple alpha rate in a hot dense medium. Phys. Rev. Lett. 119, 112701 (2017).
Meyer, B. S., Mathews, G. J., Howard, W. M., Woosley, S. E. & Hoffman, R. D. r-process nucleosynthesis in the high-entropy supernova bubble. Astrophys. J. 399, 656–664 (1992).
Woosley, S. E. & Hoffman, R. D. The α-process and the r-process. Astrophys. J. 395, 202–239 (1992).
Hüdepohl, L., Müller, B., Janka, H. T., Marek, A. & Raffelt, G. G. Neutrino signal of electron-capture supernovae from core collapse to cooling. Phys. Rev. Lett. 104, 251101 (2010).
Fischer, T., Whitehouse, S. C., Mezzacappa, A., Thielemann, F. K. & Liebendörfer, M. Protoneutron star evolution and the neutrino-driven wind in general relativistic neutrino radiation hydrodynamics simulations. Astron. Astrophys. 517, A80 (2010).
Rayet, M., Arnould, M. & Prantzos, N. The p-process revisited. Astron. Astrophys. 227, 271–281 (1990).
Travaglio, C. et al. Galactic evolution of Sr, Y, and Zr: a multiplicity of nucleosynthetic processes. Astrophys. J. 601, 864–884 (2004).
Montes, F. et al. Nucleosynthesis in the early Galaxy. Astrophys. J. 671, 1685–1695 (2007).
Qian, Y. Z. & Wasserburg, G. J. Abundances of Sr, Y, and Zr in metal-poor stars and implications for chemical evolution in the early Galaxy. Astrophys. J. 687, 272–286 (2008).
Hansen, C. J., Montes, F. & Arcones, A. How many nucleosynthesis processes exist at low metallicity? Astrophys. J. 797, 123 (2014).
Eichler, M. et al. Nucleosynthesis in 2D core-collapse supernovae of 11.2 and 17.0 M☉ progenitors: implications for Mo and Ru production. J. Phys. G 45, 014001 (2018).
Bliss, J., Arcones, A. & Qian, Y. Z. Production of Mo and Ru isotopes in neutrino-driven winds: implications for solar abundances and presolar grains. Astrophys. J. 866, 105 (2018).
Angulo, C. et al. A compilation of charged-particle induced thermonuclear reaction rates. Nucl. Phys. A 656, 3–183 (1999).
Arcones, A. & Thielemann, F.-K. Neutrino-driven wind simulations and nucleosynthesis of heavy elements. J. Phys. G 40, 013201 (2013).
Hoffman, R. D., Woosley, S. E. & Qian, Y. Z. Nucleosynthesis in neutrino-driven winds. II. Implications for heavy element synthesis. Astrophys. J. 482, 951–962 (1997).
Wanajo, S., Müller, B., Janka, H.-T. & Heger, A. Nucleosynthesis in the innermost ejecta of neutrino-driven supernova explosions in two dimensions. Astrophys. J. 852, 40 (2018).
Davids, C. N. & Bonner, T. Enhancement of the 3 4He → 12C reaction rate by inelastic proton scattering. Astrophys. J. 166, 405–410 (1971).
Freer, M., Horiuchi, H., Kanada-En’yo, Y., Lee, D. & Meißner, U.-G. Microscopic clustering in light nuclei. Rev. Mod. Phys. 90, 035004 (2018).
Zimmerman, W. R. et al. Unambiguous identification of the second 2+ state in 12C and the structure of the Hoyle state. Phys. Rev. Lett. 110, 152502 (2013).
Zimmerman, W. R. Direct Observation of the Second 2+ State in 12C. PhD thesis, Univ. of Connecticut (2013).
Lippuner, J. & Roberts, L. SkyNet: a modular nuclear reaction network library. Astrophys. J. Suppl. Ser. 233, 18 (2017).
Timmes, F. X. & Swesty, F. D. The accuracy, consistency, and speed of an electron–positron equation of state based on table interpolation of the Helmholtz free energy. Astrophys. J. Suppl. Ser. 126, 501–516 (2000).
Cyburt, R. H. et al. The JINA REACLIB database: its recent updates and impact on type-I X-ray bursts. Astrophys. J. 189, 240–252 (2010).
Caughlan, G. R. & Fowler, W. A. Thermonuclear reaction rates V. At. Data Nucl. Data Tables 40, 283–334 (1988).
Arnold, C. W. et al. Cross-section measurement of 9Be(γ, n)8Be and implications for α + α + n → 9Be in the r process. Phys. Rev. C 85, 044605 (2012).
Radice, D. et al. Binary neutron star mergers: mass ejection, electromagnetic counterparts, and nucleosynthesis. Astrophys. J. 869, 130 (2018).
Roberts, L. et al. The influence of neutrinos on r-process nucleosynthesis in the ejecta of black hole-neutron star mergers. Mon. Not. R. Astron. Soc. 464, 3907 (2017).
We thank A. Arcones, J. Bliss, H. O. U. Fynbo, G. M. Hale, D. Lee and H. Weller for discussions. We acknowledge support from NSF awards PHY-1430152 (JINA Center for the Evolution of the Elements), PHY-1913554 and PHY-1102511. S.J. is supported by CSC-FRIB Postdoctoral Fellowship grant 201600090331. L.F.R. was partially supported by the US Department of Energy through the Advanced Computing (SciDAC) programme under award number DE-SC0017955.
The authors declare no competing interests.
Peer review information Nature thanks the anonymous reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Jin, S., Roberts, L.F., Austin, S.M. et al. Enhanced triple-α reaction reduces proton-rich nucleosynthesis in supernovae. Nature 588, 57–60 (2020). https://doi.org/10.1038/s41586-020-2948-7