Proposed mechanisms for the production of calcium in the first stars (population III stars)—primordial stars that formed out of the matter of the Big Bang—are at odds with observations1. Advanced nuclear burning and supernovae were thought to be the dominant source of the calcium production seen in all stars2. Here we suggest a qualitatively different path to calcium production through breakout from the ‘warm’ carbon–nitrogen–oxygen (CNO) cycle through a direct experimental measurement of the 19F(p, γ)20Ne breakout reaction down to a very low energy point of 186 kiloelectronvolts, reporting a key resonance at 225 kiloelectronvolts. In the domain of astrophysical interest2, at around 0.1 gigakelvin, this thermonuclear 19F(p, γ)20Ne rate is up to a factor of 7.4 larger than the previous recommended rate3. Our stellar models show a stronger breakout during stellar hydrogen burning than previously thought1,4,5, and may reveal the nature of calcium production in population III stars imprinted on the oldest known ultra-iron-poor star, SMSS0313-67086. Our experimental result was obtained in the China JinPing Underground Laboratory7, which offers an environment with an extremely low cosmic-ray-induced background8. Our rate showcases the effect that faint population III star supernovae can have on the nucleosynthesis observed in the oldest known stars and first galaxies, which are key mission targets of the James Webb Space Telescope9.
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Experimental data taken at JUNA are proprietary to the collaboration but can be made available from the corresponding authors upon reasonable request.
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We thank the staff of the CJPL and Yalong River Hydropower Development Company (N. C. Qi, W. L. Sun, X. Y. Guo, P. Zhang, Y. H. Chen, Y. Zhou, J. F. Zhou, J. R. He, C. S. Shang, M. C. Li) for logistics support. We thank F. Herwig, Y. Sun and S. E. Malek for discussions. We acknowledge support from the National Natural Science Foundation of China (nos. 11825504, 11490560, 12075027, 12125509). R.J.dB. and M.W. were supported by the NSF through grant no. Phys-2011890. R.J.dB., M.W. and A.H. were supported by the Joint Institute for Nuclear Astrophysics through grant no. PHY-1430152 (JINA Center for the Evolution of the Elements). A.H. was supported by the Australian Research Council (ARC) Centre of Excellence (CoE) for Gravitational Wave Discovery (OzGrav) through project number CE170100004, by the ARC CoE for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) through project number CE170100013. D.K. acknowledges the support of the Romanian Ministry of Research and Innovation under research contract 10N/PN 19 06 01 05. D.O. was supported by the NSF through grant no. OAC-2004601.
The authors declare no competing interests.
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Extended data figures and tables
The proton beam bombarded on the implanted 19F target through two apertures. The beam spot on the last aperture was monitored by a camera. A LN2-cooled trap extended close to the target to reduce the carbon build-up. The γ-rays were detected by a 4π BGO array with massive shielding.
Left, Typical γ-ray spectra taken with a 4π BGO array at JUNA during proton bombardment of an implanted 19F target, at proton energies of (a) 356 keV and (b) 250 keV. The heavy γ-ray background from the competing 19F(p, αγ)16O channel and their summing signals are indicated. The summing γ-ray peak for the target 19F(p, γ)20Ne channel is indicated by red arrows. The inset shows the coincident γ-ray spectrum gated on the summing peak located in the shaded region. Right, The corresponding level scheme, where the summing γ-ray and the gated γ-ray transitions are illustrated by the coloured arrows.
Extended Data Fig. 3 Yield ratios of (p, αγ)/(p, γ1) and (p, αγ)/(p, γ0) over the 323-keV resonance.
Top, (p, αγ)/(p, γ0); bottom, (p, αγ)/(p, γ1). The weighted average ratios and the associated uncertainties are plotted as solid and dashed lines, respectively. Only statistical errors are shown.
The vertical dashed lines indicate 16%, 50% and 84% quantiles. Here ‘sub’ refers to the sub-threshold state at Ex = 12.396 MeV, ‘thresh’ the near-threshold state at Ex = 12.855 MeV, and ‘npα’ and ‘npγ’ are the normalization factors for the (p, α) and (p, γ) datasets, respectively. Uniform priors were taken for all parameters of the analysis.
This Supplementary Information file introduces the astrophysical context of the present work, and describes the calculation results based on three stellar models. Some remarks are included at the end for an outlook.
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Zhang, L., He, J., deBoer, R.J. et al. Measurement of 19F(p, γ)20Ne reaction suggests CNO breakout in first stars. Nature 610, 656–660 (2022). https://doi.org/10.1038/s41586-022-05230-x