The first stars that formed after the Big Bang were probably massive1, and they provided the Universe with the first elements heavier than helium (‘metals’), which were incorporated into low-mass stars that have survived to the present2,3. Eight stars in the oldest globular cluster in the Galaxy, NGC 6522, were found to have surface abundances consistent with the gas from which they formed being enriched by massive stars4 (that is, with higher α-element/Fe and Eu/Fe ratios than those of the Sun). However, the same stars have anomalously high abundances of Ba and La with respect to Fe4, which usually arises through nucleosynthesis in low-mass stars5 (via the slow-neutron-capture process, or s-process). Recent theory suggests that metal-poor fast-rotating massive stars are able to boost the s-process yields by up to four orders of magnitude6, which might provide a solution to this contradiction. Here we report a reanalysis of the earlier spectra, which reveals that Y and Sr are also overabundant with respect to Fe, showing a large scatter similar to that observed in extremely metal-poor stars7, whereas C abundances are not enhanced. This pattern is best explained as originating in metal-poor fast-rotating massive stars, which might point to a common property of the first stellar generations and even of the ‘first stars’.
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C.C., U.F., G.M., T.D. and A.M. acknowledge support from the Swiss National Science Foundation (SNSF). M.P. acknowledges support from an Ambizione grant from the SNSF, and from NSF grant PHY 02-16783 (Joint Institute for Nuclear Astrophysics, JINA). B.B. acknowledges support from FAPESP and CNPq (Brazil). C.C. and T.D. acknowledge partial support from ESF-EuroGENESIS. R.H. acknowledges support from the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan. This work is based on observations collected at the European Southern Observatory (ESO).
The authors declare no competing financial interests.
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Chiappini, C., Frischknecht, U., Meynet, G. et al. Imprints of fast-rotating massive stars in the Galactic Bulge. Nature 472, 454–457 (2011). https://doi.org/10.1038/nature10000
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