The chemical composition of the most metal-deficient stars largely reflects the composition of the gas from which they formed. These old stars provide crucial clues to the star formation history and the synthesis of chemical elements in the early Universe. They are the local relics of epochs otherwise observable only at very high redshifts1,2; if totally metal-free (‘population III’) stars could be found, this would allow the direct study of the pristine gas from the Big Bang. Earlier searches for such stars found none with an iron abundance less than 1/10,000 that of the Sun3,4, leading to the suggestion5,6 that low-mass stars could form from clouds above a critical iron abundance. Here we report the discovery of a low-mass star with an iron abundance as low as 1/200,000 of the solar value. This discovery suggests that population III stars could still exist—that is, that the first generation of stars also contained long-lived low-mass objects. The previous failure to find them may be an observational selection effect.
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We thank the European Southern Observatory for providing us with reduced UVES spectra. We are grateful to M. Asplund, B. Edvardsson, J. Lattanzio, J. Norris, N. Piskunov, B. Plez, D. Reimers, S.G. Ryan, L. Siess and L. Wisotzki for their contributions and suggestions. N.C. acknowledges a Marie Curie Fellowship granted by the European Commission, and support from Deutsche Forschungsgemeinschaft. T.C.B. acknowledges grants of the US National Science Foundation, S.R. support from FAPESP and CNPq, and the Uppsala group from the Swedish Research Council.
The authors declare that they have no competing financial interests.
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Christlieb, N., Bessell, M., Beers, T. et al. A stellar relic from the early Milky Way. Nature 419, 904–906 (2002). https://doi.org/10.1038/nature01142