Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

An age difference of two billion years between a metal-rich and a metal-poor globular cluster

Abstract

Globular clusters trace the formation history of the spheroidal components of our Galaxy and other galaxies1, which represent the bulk of star formation over the history of the Universe2. The clusters exhibit a range of metallicities (abundances of elements heavier than helium), with metal-poor clusters dominating the stellar halo of the Galaxy, and higher-metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk3,4. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and were later engulfed along with their original host galaxies, and which were formed within it. Here we report an absolute age of 9.9 ± 0.7 billion years (at 95 per cent confidence) for the metal-rich globular cluster 47 Tucanae, determined by modelling the properties of the cluster’s white-dwarf cooling sequence. This is about two billion years younger than has been inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evidence that metal-rich clusters like 47 Tucanae formed later than metal-poor halo clusters like NGC 6397.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: The 47 Tucanae white-dwarf cooling sequence.
Figure 2: Luminosity function comparison between 47 Tucanae and NGC 6397.
Figure 3: Model comparison to white-dwarf colour-magnitude distribution.
Figure 4: Age–metallicity relation based on white dwarfs.

Similar content being viewed by others

References

  1. Brodie, J. P. & Strader, J. Extragalactic globular clusters and galaxy formation. Annu. Rev. Astron. Astrophys. 44, 193–267 (2006)

    Article  ADS  CAS  Google Scholar 

  2. Fukugita, M., Hogan, C. J. & Peebles, P. J. E. The cosmic baryon budget. Astrophys. J. 503, 518–530 (1998)

    Article  ADS  CAS  Google Scholar 

  3. Zinn, R. The globular cluster system of the galaxy. IV—The halo and disk subsystems. Astrophys. J. 293, 424–444 (1985)

    Article  ADS  CAS  Google Scholar 

  4. Minniti, D. Metal-rich globular clusters with R less than or equal 3 kpc: disk or bulge clusters. Astron. J. 109, 1663–1669 (1995)

    Article  ADS  Google Scholar 

  5. Salaris, M. & Weiss, A. Metal-rich globular clusters in the galactic disk: new age determinations and the relation to halo clusters. Astron. Astrophys. 335, 943–953 (1998)

    ADS  CAS  Google Scholar 

  6. Rosenberg, A., Saviane, I., Piotto, G. & Aparicio, A. Galactic globular cluster relative ages. Astron. J. 118, 2306–2320 (1999)

    Article  ADS  CAS  Google Scholar 

  7. De Angeli, F. et al. Galactic globular cluster relative ages. Astron. J. 130, 116–125 (2005)

    Article  ADS  CAS  Google Scholar 

  8. Marín-Franch, A. et al. The ACS survey of galactic globular clusters. VII. Relative ages. Astrophys. J. 694, 1498–1516 (2009)

    Article  ADS  Google Scholar 

  9. Dotter, A., Sarajedini, A. & Anderson, J. Globular clusters in the Outer Galactic Halo: new Hubble Space Telescope/Advanced Camera for Surveys imaging of six globular clusters and the Galactic Globular Cluster age-metallicity relation. Astrophys. J. 738, 74–84 (2011)

    Article  ADS  Google Scholar 

  10. Hansen, B. et al. The white dwarf cooling sequence of the globular cluster Messier 4. Astrophys. J. 574, L155–L158 (2002)

    Article  ADS  Google Scholar 

  11. Hansen, B. et al. Hubble Space Telescope observations of the white dwarf cooling sequence of M4. Astrophys. J. 155 (Suppl.). 551–576 (2004)

    Article  Google Scholar 

  12. Hansen, B. et al. The white dwarf cooling sequence of NGC 6397, 2007. Astrophys. J. 671, 380–401 (2007)

    Article  ADS  CAS  Google Scholar 

  13. Bedin, L. R. et al. The end of the white dwarf cooling sequence in M4: An efficient approach. Astrophys. J. 697, 965–979 (2009)

    Article  ADS  Google Scholar 

  14. Koch, A. & McWilliam, A. A new abundance scale for the globular cluster 47 Tuc. Astron. J. 135, 1551–1566 (2008)

    Article  ADS  CAS  Google Scholar 

  15. McWilliam, A. & Bernstein, R. A. Globular cluster abundances from high-resolution integrated-light spectra. I. 47 Tuc. Astrophys. J. 684, 326–347 (2008)

    Article  ADS  CAS  Google Scholar 

  16. Carretta, E. et al. Intrinsic iron spread and a new metallicity scale for globular clusters. Astron. Astrophys. 508, 695–706 (2009)

    Article  ADS  CAS  Google Scholar 

  17. Paxton, B. et al. Modules for experiments in stellar astrophysics (MESA). Astrophys. J. 192 (Suppl.). 3–37 (2011)

    Article  Google Scholar 

  18. Milone, A. et al. Multiple stellar populations in 47 Tucanae. Astrophys. J. 744, 58–79 (2012)

    Article  ADS  Google Scholar 

  19. Dotter, A. et al. The ACS survey of galactic globular clusters. II. Stellar evolution tracks, isochrones, luminosity functions, and synthetic horizontal-branch models. Astron. J. 134, 376–390 (2007)

    Article  ADS  CAS  Google Scholar 

  20. Gratton, R. G. et al. Distances and ages of NGC 6397, NGC 6752 and 47 Tuc. Astron. Astrophys. 408, 529–543 (2003)

    Article  ADS  Google Scholar 

  21. VandenBerg, D. A. Models for old, metal-poor stars with enhanced -element abundances. II. Their implications for the ages of the galaxy's globular clusters and field halo stars. Astrophys. J. 129 (Suppl.). 315–352 (2000)

    Article  ADS  CAS  Google Scholar 

  22. Salaris, M. & Weiss, A. Homogeneous age dating of 55 Galactic globular clusters. Clues to the Galaxy formation mechanisms. Astron. Astrophys. 388, 492–503 (2002)

    Article  ADS  Google Scholar 

  23. Salaris, M. et al. Deep near-infrared photometry of the globular cluster 47 Tucanae. Reconciling theory and observations. Astron. Astrophys. 476, 243–253 (2007)

    Article  ADS  CAS  Google Scholar 

  24. Thompson, Y. B. et al. The Cluster AgeS Experiment (CASE). IV. Analysis of the eclipsing binary V69 in the globular cluster 47 Tuc. Astron. J. 139, 329–341 (2010)

    Article  ADS  CAS  Google Scholar 

  25. Muratov, A. L. & Gnedin, O. Y. Modeling the metallicity distribution of globular clusters. Astrophys. J. 718, 1266 (2010)

    Article  ADS  Google Scholar 

  26. Shapiro, K. L., Genzel, R. & Förster Schreiber, N. M. Star-forming galaxies at z2 and the formation of the metal-rich globular cluster population. Mon. Not. R. Astron. Soc. 403, L36–L40 (2010)

    Article  ADS  Google Scholar 

  27. Tonini, C. The metallicity bimodality of globular cluster systems: a test of galaxy assembly and the evolution of the galaxy mass-metallicity relation. Astrophys. J. 762, 39–50 (2013)

    Article  ADS  Google Scholar 

  28. García-Berro, E. et al. A white dwarf cooling age of 8Gyr for NGC 6791 from physical separation processes. Nature 465, 194–196 (2010)

    Article  ADS  Google Scholar 

  29. Valenti, J. A. & Fischer, D. A. Spectroscopic properties of cool stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT planet search programs. Astrophys. J. 159 (Supp.). 141–166 (2005)

    Article  ADS  CAS  Google Scholar 

  30. Wright, E. L. A cosmology calculator for the World Wide Web. Pub. Astron. Soc. Pacif. 118, 1711–1715 (2006)

    Article  ADS  Google Scholar 

Download references

Acknowledgements

Support for the programme GO-11677 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work is supported in part by the Natural Science and Engineering Research Council of Canada.

Author information

Authors and Affiliations

Authors

Contributions

B.M.S.H. and A.D were primarily responsible for the modelling efforts. J.S.K. and J.A. were primarily responsible for the analysis of the data. H.B.R., R.M.R. and D.R. were responsible for the scheduling of the observations. All authors, including M.M.S., G.G.F., J.R.H., I.R.K. and P.B.S. were involved in the conception and planning of the project and in the writing of the paper.

Corresponding author

Correspondence to B. M. S. Hansen.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text, Supplementary Figures 1-6 and Supplementary References. (PDF 888 kb)

PowerPoint slides

Rights and permissions

Reprints and permissions

About this article

Cite this article

Hansen, B., Kalirai, J., Anderson, J. et al. An age difference of two billion years between a metal-rich and a metal-poor globular cluster. Nature 500, 51–53 (2013). https://doi.org/10.1038/nature12334

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature12334

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing