The exclusion of a significant range of ages in a massive star cluster



Stars spend most of their lifetimes on the main sequence in the Hertzsprung–Russell diagram. The extended main-sequence turn-off regions—containing stars leaving the main sequence after having spent all of the hydrogen in their cores—found in massive (more than a few tens of thousands of solar masses), intermediate-age (about one to three billion years old) star clusters1,2,3,4,5,6,7,8 are usually interpreted as evidence of internal age spreads of more than 300 million years2,4,5, although young clusters are thought to quickly lose any remaining star-forming fuel following a period of rapid gas expulsion on timescales of order 107 years9,10. Here we report, on the basis of a combination of high-resolution imaging observations and theoretical modelling, that the stars beyond the main sequence in the two-billion-year-old cluster NGC 1651, characterized by a mass of about 1.7 × 105 solar masses3, can be explained only by a single-age stellar population, even though the cluster has a clearly extended main-sequence turn-off region. The most plausible explanation for the existence of such extended regions invokes a population of rapidly rotating stars, although the secondary effects of the prolonged stellar lifetimes associated with such a stellar population mixture are as yet poorly understood. From preliminary analysis of previously obtained data, we find that similar morphologies are apparent in the Hertzsprung–Russell diagrams of at least five additional intermediate-age star clusters2,3,5,11, suggesting that an extended main-sequence turn-off region does not necessarily imply the presence of a significant internal age dispersion.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: NGC 1651’s stellar distribution in colour–magnitude space.
Figure 2: Comparison of the observed stellar distribution with the expectations of a 450 Myr spread in cluster internal age.
Figure 3: Comparison of the numbers of stars in NGC 1651 at selected evolutionary stages.
Figure 4: Expected age distributions resulting from the cluster’s turn-off and subgiant-branch stars.


  1. 1

    Mackey, A. D. & Broby Nielsen, P. A double main-sequence turn-off in the rich star cluster NGC 1846 in the Large Magellanic Cloud. Mon. Not. R. Astron. Soc. 379, 151–158 (2007)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Mackey, A. D., Broby Nielsen, P., Ferguson, A. M. N. & Richardson, J. C. Multiple stellar populations in three rich Large Magellanic Cloud star clusters. Astrophys. J. 681, L17–L20 (2008)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Milone, A. P., Bedin, L. R., Piotto, G. & Anderson, J. Multiple stellar populations in Magellanic Cloud clusters. I. An ordinary feature for intermediate age globulars in the LMC? Astron. Astrophys. 497, 755–771 (2009)

    ADS  Article  Google Scholar 

  4. 4

    Rubele, S., Kerber, L. & Girardi, L. The star-formation history of the Small Magellanic Cloud star cluster NGC 419. Mon. Not. R. Astron. Soc. 403, 1156–1164 (2010)

    ADS  CAS  Article  Google Scholar 

  5. 5

    Goudfrooij, P., Puzia, T. H., Kozhurina-Platais, V. & Chandar, R. Population parameters of intermediate-age star clusters in the Large Magellanic Cloud. II. New insights from extended main-sequence turnoffs in seven star clusters. Astrophys. J. 737, 3 (2011)

    ADS  Article  Google Scholar 

  6. 6

    Keller, S. C., Mackey, A. D. & Da Costa, G. S. Extended star formation in the intermediate-age Large Magellanic Cloud star cluster NGC 2209. Astrophys. J. 761, L5 (2012)

    ADS  Article  Google Scholar 

  7. 7

    Rubele, S. et al. The star formation history of the Large Magellanic Cloud star clusters NGC 1846 and NGC 1783. Mon. Not. R. Astron. Soc. 430, 2774–2788 (2013)

    ADS  Article  Google Scholar 

  8. 8

    Li, C., de Grijs, R. & Deng, L. Not-so-simple stellar populations in the intermediate-age Large Magellanic Cloud star clusters NGC 1831 and NGC 1868. Astrophys. J. 784, 157 (2014)

    ADS  Article  Google Scholar 

  9. 9

    Bastian, N. & Goodwin, S. P. Evidence for the strong effect of gas removal on the internal dynamics of young stellar clusters. Mon. Not. R. Astron. Soc. 369, L9–L13 (2006)

    ADS  Article  Google Scholar 

  10. 10

    Longmore, S. N. et al. in Protostars and Planets VI (eds Beuther, H. Klessen, R., Dullermond, C. & Henning, Th. ) (Univ. Arizona Press, in the press); preprint at (2014)

  11. 11

    Piatti, A. E., Keller, S. C., Mackey, A. D. & Da Costa, G. S. Gemini/GMOS photometry of intermediate-age star clusters in the Large Magellanic Cloud. Mon. Not. R. Astron. Soc. 444, 1425–1441 (2014)

    ADS  Article  Google Scholar 

  12. 12

    Piotto, G. et al. Metallicities on the double main sequence of ω Centauri imply large helium enhancement. Astrophys. J. 621, 777–784 (2005)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Piotto, G. et al. A triple main sequence in the globular cluster NGC 2808. Astrophys. J. 661, L53–L56 (2007)

    ADS  CAS  Article  Google Scholar 

  14. 14

    Sollima, A. et al. Deep FORS1 observations of the double main sequence of ω Centauri. Astrophys. J. 654, 915–922 (2007)

    ADS  Article  Google Scholar 

  15. 15

    Milone, A. P. et al. The ACS Survey of Galactic Globular Clusters. III. The double subgiant branch of NGC 1851. Astrophys. J. 673, 241–250 (2008)

    ADS  Article  Google Scholar 

  16. 16

    Lee, J.-W., Kang, Y.-W., Lee, J. & Lee, Y.-W. Enrichment by supernovae in globular clusters with multiple populations. Nature 462, 480–482 (2009)

    ADS  CAS  Article  Google Scholar 

  17. 17

    Milone, A. P. et al. A double main sequence in the globular cluster NGC 6397. Astrophys. J. 745, 27 (2012)

    ADS  Article  Google Scholar 

  18. 18

    Piotto, G. et al. Multi-wavelength Hubble Space Telescope photometry of stellar populations in NGC 288. Astrophys. J. 775, 15 (2013)

    ADS  Article  Google Scholar 

  19. 19

    Marigo, P. et al. Evolution of asymptotic giant branch stars. II. Optical to far-infrared isochrones with improved TP-AGB models. Astron. Astrophys. 482, 883–905 (2008)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Dirsch, B., Richtler, T., Gieren, W. P. & Hilker, M. Age and metallicity for six LMC clusters and their surrounding field population. Astron. Astrophys. 360, 133–160 (2000)

    ADS  CAS  Google Scholar 

  21. 21

    Grocholski, A. J., Sarajedini, A., Olsen, K. A. G., Tiede, G. P. & Mancone, C. L. Distances to populous clusters in the Large Magellanic Cloud via the K-band luminosity of the red clump. Astrophys. J. 134, 680–693 (2007)

    ADS  CAS  Google Scholar 

  22. 22

    Hu, Y., Deng, L., de Grijs, R., Liu, Q. & Goodwin, S. P. The binary fraction of the young cluster NGC 1818 in the Large Magellanic Cloud. Astrophys. J. 724, 649–656 (2010)

    ADS  Article  Google Scholar 

  23. 23

    Li, C., de Grijs, R. & Deng, L. The binary fractions in the massive young Large Magellanic Cloud star clusters NGC 1805 and NGC 1818. Mon. Not. R. Astron. Soc. 436, 1497–1512 (2013)

    ADS  Article  Google Scholar 

  24. 24

    Bastian, N. & de Mink, S. E. The effect of stellar rotation on colour–magnitude diagrams: on the apparent presence of multiple populations in intermediate age stellar clusters. Mon. Not. R. Astron. Soc. 398, L11–L15 (2009)

    ADS  Article  Google Scholar 

  25. 25

    Li, Z., Mao, C., Chen, L. & Zhang, Q. Combined effects of binaries and stellar rotation on the color–magnitude diagrams of intermediate-age star clusters. Astrophys. J. 761, L22 (2012)

    ADS  Article  Google Scholar 

  26. 26

    Yang, W., Bi, S., Meng, X. & Liu, Z. The effects of rotation on the main-sequence turnoff of intermediate-age massive star clusters. Astrophys. J. 776, 112 (2013)

    ADS  Article  Google Scholar 

  27. 27

    Girardi, L., Eggenberger, P. & Miglio, A. Can rotation explain the multiple main-sequence turn-offs of Magellanic Cloud star clusters? Mon. Not. R. Astron. Soc. 412, L103–L107 (2011)

    ADS  Article  Google Scholar 

  28. 28

    Georgy, C. et al. Populations of rotating stars. III. SYCLIST, the new Geneva population synthesis code. Astron. Astrophys. 566, A21 (2014)

    Article  Google Scholar 

  29. 29

    Davis, L. E. A Reference Guide to the IRAF/DAOPHOT Package. (1994)

  30. 30

    Elson, R. A. W., Fall, S. M. & Freeman, K. C. The stellar content of rich young clusters in the Large Magellanic Cloud. Astrophys. J. 336, 734–751 (1989)

    ADS  Article  Google Scholar 

  31. 31

    Mackey, A. D. & Gilmore, G. F. Surface brightness profiles and structural parameters for 53 rich stellar clusters in the Large Magellanic Cloud. Mon. Not. R. Astron. Soc. 338, 85–119 (2003)

    ADS  Article  Google Scholar 

  32. 32

    Bekki, K. & Mackey, A. D. On the origin of double main-sequence turn-offs in star clusters of the Magellanic Clouds. Mon. Not. R. Astron. Soc. 394, 124–132 (2009)

    ADS  Article  Google Scholar 

  33. 33

    Mestel, L. & Spruit, H. C. On magnetic braking of late-type stars. Mon. Not. R. Astron. Soc. 226, 57–66 (1987)

    ADS  Article  Google Scholar 

  34. 34

    Royer, F., Zorec, J. & Gómez, A. E. Rotational velocities of A-type stars. III. Velocity distributions. Astron. Astrophys. 463, 671–682 (2007)

    ADS  Article  Google Scholar 

  35. 35

    Mucciarelli, A., Carretta, E., Origlia, L. & Ferraro, F. R. The chemical composition of red giant stars in four intermediate-age clusters of the Large Magellanic Cloud. Astron. J. 136, 375–388 (2008)

    ADS  CAS  Article  Google Scholar 

  36. 36

    Mucciarelli, A., Dalessandro, E., Ferraro, F. R., Origlia, L. & Lanzoni, B. No evidence of chemical anomalies in the bimodal turnoff cluster NGC 1806 in the Large Magellanic Cloud. Astrophys. J. 793, L6 (2014)

    ADS  Article  Google Scholar 

  37. 37

    Carretta, E. et al. Properties of stellar generations in globular clusters and relations with global parameters. Astron. Astrophys. 516, A55 (2010)

    Article  Google Scholar 

  38. 38

    Bastian, N. & Strader, J. Constraining globular cluster formation through studies of young massive clusters. III. A lack of gas and dust in massive stellar clusters in the LMC and SMC. Mon. Not. R. Astron. Soc. 443, 3594–3600 (2014)

    ADS  CAS  Article  Google Scholar 

Download references


We thank S. de Mink, Y. Huang and X. Chen for discussions and assistance. Partial financial support for this work was provided by the National Natural Science Foundation of China through grants 11073001, 11373010 and 11473037.

Author information




C.L., R.d.G. and L.D. jointly designed and coordinated this study. C.L. performed the data reduction. C.L. and R.d.G. collaborated on the detailed analysis. L.D. provided ideas that improved the study’s robustness. All authors read, commented on and jointly approved submission of this article.

Corresponding author

Correspondence to Chengyuan Li.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Radial brightness density profile of NGC 1651.

The 1σ uncertainties shown are due to Poisson noise.

Extended Data Figure 2 Background decontamination.

a, Original colour–magnitude diagram of NGC 1651. b, Field-star colour–magnitude diagram. c, Field-star-decontaminated NGC 1651 colour–magnitude diagram.

Extended Data Figure 3 Constraints on the maximum likely age dispersion.

Number distribution, N (including 1σ standard deviations), of the deviations in magnitude, ΔB, of our subgiant-branch sample, as in Fig. 2. The black dashed lines at the top indicate typical ΔB values for isochrones of different ages, as indicated.

Extended Data Figure 4 Evolutionary tracks for extremes in stellar rotation rates.

Red, non-rotating stars; blue, stellar rotation at 95% of the critical break-up rate (ω = 0.95). Both tracks apply to 1.7 solar-mass stars. , solar luminosity; Teff, effective temperature.

Extended Data Table 1 Age dispersions required to match the observed spread of subgiant-branch stars in NGC 1651

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Li, C., de Grijs, R. & Deng, L. The exclusion of a significant range of ages in a massive star cluster. Nature 516, 367–369 (2014).

Download citation

Further reading


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.