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Enhanced triple-α reaction reduces proton-rich nucleosynthesis in supernovae


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.

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Fig. 1: Enhancement of seed nuclei production.
Fig. 2: The total in-medium enhanced triple-α reaction rate.
Fig. 3: Nucleosynthesis results.
Fig. 4: Nucleosynthesis results with the rate enhancement at the upper end of the estimated nuclear uncertainty.
Fig. 5: Effect of the enhancement on p-nuclide production.

Data availability

The simulation data that support these findings is available from the corresponding author upon reasonable request.

Code availability

The reaction network library SkyNet used for this work is publicly available at The code used to run and analyse the simulations described here (which relies on the SkyNet library) is publicly available at


  1. Wanajo, S., Janka, H.-T. & Kubono, S. Uncertainties in the νp-process: supernova dynamics versus nuclear physics. Astrophys. J. 729, 46 (2011).

    Article  ADS  Google Scholar 

  2. 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).

    Article  ADS  CAS  Google Scholar 

  3. Fröhlich, C. et al. Neutrino-induced nucleosynthesis of A > 64 nuclei: the νp process. Phys. Rev. Lett. 96, 142502 (2006).

    Article  ADS  Google Scholar 

  4. 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).

    Article  ADS  CAS  Google Scholar 

  5. Wanajo, S. The rp-process in neutrino-driven winds. Astrophys. J. 647, 1323–1340 (2006).

    Article  ADS  CAS  Google Scholar 

  6. 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).

    Article  ADS  CAS  Google Scholar 

  7. Freer, M. & Fynbo, H. O. U. The Hoyle state in 12C. Prog. Part. Nucl. Phys. 78, 1–23 (2014).

    Article  ADS  CAS  Google Scholar 

  8. 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).

    Article  ADS  CAS  Google Scholar 

  9. Beard, M., Austin, S. M. & Cyburt, R. Enhancement of the triple alpha rate in a hot dense medium. Phys. Rev. Lett. 119, 112701 (2017).

    Article  ADS  Google Scholar 

  10. 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).

    Article  ADS  CAS  Google Scholar 

  11. Woosley, S. E. & Hoffman, R. D. The α-process and the r-process. Astrophys. J. 395, 202–239 (1992).

    Article  ADS  CAS  Google Scholar 

  12. 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).

    Article  ADS  Google Scholar 

  13. 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).

    Article  Google Scholar 

  14. Rayet, M., Arnould, M. & Prantzos, N. The p-process revisited. Astron. Astrophys. 227, 271–281 (1990).

    ADS  CAS  Google Scholar 

  15. Travaglio, C. et al. Galactic evolution of Sr, Y, and Zr: a multiplicity of nucleosynthetic processes. Astrophys. J. 601, 864–884 (2004).

    Article  ADS  CAS  Google Scholar 

  16. Montes, F. et al. Nucleosynthesis in the early Galaxy. Astrophys. J. 671, 1685–1695 (2007).

    Article  ADS  CAS  Google Scholar 

  17. 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).

    Article  ADS  CAS  Google Scholar 

  18. Hansen, C. J., Montes, F. & Arcones, A. How many nucleosynthesis processes exist at low metallicity? Astrophys. J. 797, 123 (2014).

    Article  ADS  Google Scholar 

  19. 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).

    Article  ADS  Google Scholar 

  20. 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).

    Article  ADS  Google Scholar 

  21. Angulo, C. et al. A compilation of charged-particle induced thermonuclear reaction rates. Nucl. Phys. A 656, 3–183 (1999).

    Article  ADS  Google Scholar 

  22. Arcones, A. & Thielemann, F.-K. Neutrino-driven wind simulations and nucleosynthesis of heavy elements. J. Phys. G 40, 013201 (2013).

    Article  ADS  Google Scholar 

  23. 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).

    Article  ADS  CAS  Google Scholar 

  24. 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).

    Article  ADS  Google Scholar 

  25. Davids, C. N. & Bonner, T. Enhancement of the 3 4He → 12C reaction rate by inelastic proton scattering. Astrophys. J. 166, 405–410 (1971).

    Article  ADS  CAS  Google Scholar 

  26. Freer, M., Horiuchi, H., Kanada-En’yo, Y., Lee, D. & Meißner, U.-G. Microscopic clustering in light nuclei. Rev. Mod. Phys. 90, 035004 (2018).

    Article  ADS  MathSciNet  CAS  Google Scholar 

  27. 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).

    Article  ADS  CAS  Google Scholar 

  28. Zimmerman, W. R. Direct Observation of the Second 2+ State in 12C. PhD thesis, Univ. of Connecticut (2013).

  29. Lippuner, J. & Roberts, L. SkyNet: a modular nuclear reaction network library. Astrophys. J. Suppl. Ser. 233, 18 (2017).

    Article  ADS  Google Scholar 

  30. 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).

    Article  ADS  Google Scholar 

  31. 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).

    Article  CAS  Google Scholar 

  32. Caughlan, G. R. & Fowler, W. A. Thermonuclear reaction rates V. At. Data Nucl. Data Tables 40, 283–334 (1988).

    Article  ADS  CAS  Google Scholar 

  33. Arnold, C. W. et al. Cross-section measurement of 9Be(γ, n)8Be and implications for α + α + n9Be in the r process. Phys. Rev. C 85, 044605 (2012).

    Article  ADS  Google Scholar 

  34. Radice, D. et al. Binary neutron star mergers: mass ejection, electromagnetic counterparts, and nucleosynthesis. Astrophys. J. 869, 130 (2018).

    Article  ADS  CAS  Google Scholar 

  35. 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).

    Article  ADS  CAS  Google Scholar 

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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.

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S.J. and L.F.R. carried out the calculations and analysis. S.M.A. carried out enhancement factor calculations. All authors contributed to the motivation, analysis and interpretation as well as the writing of the manuscript.

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Correspondence to Luke F. Roberts.

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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).

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