Enrichment by supernovae in globular clusters with multiple populations


The most massive globular cluster in the Milky Way, ω Centauri, is thought to be the remaining core of a disrupted dwarf galaxy1,2, as expected within the model of hierarchical merging3,4. It contains several stellar populations having different heavy elemental abundances supplied by supernovae5—a process known as metal enrichment. Although M 22 appears to be similar to ω Cen6, other peculiar globular clusters do not7,8. Therefore ω Cen and M 22 are viewed as exceptional, and the presence of chemical inhomogeneities in other clusters is seen as ‘pollution’ from the intermediate-mass asymptotic-giant-branch stars expected in normal globular clusters9. Here we report Ca abundances for seven globular clusters and compare them to ω Cen. Calcium and other heavy elements can only be supplied through numerous supernovae explosions of massive stars in these stellar systems10, but the gravitational potentials of the present-day clusters cannot preserve most of the ejecta from such explosions11. We conclude that these globular clusters, like ω Cen, are most probably the relics of more massive primeval dwarf galaxies that merged and disrupted to form the proto-Galaxy.

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Figure 1: Colour–magnitude diagrams for M 22.
Figure 2: Colour–magnitude diagrams for ω Cen, M 22, NGC 1851, NGC 2808, M 4, M 5, NGC 6752 and NGC 6397.
Figure 3: Differences in chemical compositions between double RGB sequences in M 22 and NGC 1851.


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J.-W.L. thanks A. Walker for providing the CTIO Ca filter transmission curve, D. Yong for NGC 1851 spectroscopic data before publication, and A. Yushchenko for discussions on spectrum synthesis. Support for this work was provided by the National Research Foundation of Korea to the Astrophysical Research Center for the Structure and Evolution of the Cosmos (ARCSEC). This work was based on observations made with the CTIO 1.0-m telescope, which is operated by the SMARTS consortium.

Author Contributions J.-W.L. performed observations, data analysis, interpretation, model simulations and writing of the manuscript; Y.-W.K. participated in observation planning; and J.L. performed part of the observations and data analysis. Y.-W. L. performed interpretation and writing of the manuscript. All authors discussed the results and commented on the manuscript.

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Correspondence to Jae-Woo Lee or Young-Wook Lee.

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Lee, J., Kang, Y., Lee, J. et al. Enrichment by supernovae in globular clusters with multiple populations. Nature 462, 480–482 (2009). https://doi.org/10.1038/nature08565

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