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Multiple stellar populations in the globular cluster ω Centauri as tracers of a merger event

Abstract

The discovery of the Sagittarius dwarf galaxy1, which is being tidally disrupted by and merging with the Milky Way, supports the view that the halo of the Galaxy has been built up at least partially by the accretion of similar dwarf systems. The Sagittarius dwarf contains several distinct populations of stars2,3, and includes M54 as its nucleus, which is the second most massive globular cluster associated with the Milky Way. The most massive globular cluster is ω Centauri, and here we report that ω Centauri also has several distinct stellar populations, as traced by red-giant-branch stars. The most metal-rich red-giant-branch stars are about 2 Gyr younger than the dominant metal-poor component, indicating that ω Centauri was enriched over this timescale. The presence of more than one epoch of star formation in a globular cluster is quite surprising, and suggests that ω Centauri was once part of a more massive system that merged with the Milky Way, as the Sagittarius dwarf galaxy is in the process of doing now. Mergers probably were much more frequent in the early history of the Galaxy and ω Centauri appears to be a relict of this era.

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Figure 1: Colour–magnitude diagram of 50,129 stars in the direction of ω Cen.
Figure 2: Histogram of the distribution of colour difference.
Figure 3: Stellar population models.

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Acknowledgements

Support for this work was provided by the Creative Research Initiatives Program of the Korean Ministry of Science & Technology, and in part, by the Korea Science & Engineering Foundation. S.-C.R. was a visiting astronomer at CTIO/NOAO, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.

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Correspondence to Y.-W. Lee.

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Lee, YW., Joo, JM., Sohn, YJ. et al. Multiple stellar populations in the globular cluster ω Centauri as tracers of a merger event. Nature 402, 55–57 (1999). https://doi.org/10.1038/46985

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