Skip to main content

Thank you for visiting 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.

Galaxies appear simpler than expected


Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment and feedback from supernova explosions and supermassive black holes1. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter2,3,4. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular momentum, baryon fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free from optical selection effects5, shows five independent correlations among six independent observables, despite having a wide range of properties. This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our data set. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter model in cosmology6.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Scatter plots showing correlations between five measured variables, not including colour.
Figure 2: Scatter plots showing correlations between the five measured variables and the principal components.
Figure 3: Scatter plots showing correlations between the previous five measured variables (Fig. 1), but now including colour.
Figure 4: Scatter plots showing correlations between all the six measured variables (including colour) and the principal components.


  1. 1

    de Jong, R. S. (ed.) Island Universes: Structure and Evolution of Disk Galaxies (Astrophys. Space Sci. Proc., Springer, 2007)

    Book  Google Scholar 

  2. 2

    Baugh, C. M. A primer on hierarchical galaxy formation: the semi-analytical approach. Rep. Prog. Phys. 69, 3101–3156 (2006)

    ADS  Article  Google Scholar 

  3. 3

    Dalcanton, J. J., Spergel, D. N. & Summers, I. J. The formation of disk galaxies. Astrophys. J. 482, 659–676 (1997)

    ADS  Article  Google Scholar 

  4. 4

    Mo, H. J., Mao, S. & White, S. D. M. The formation of galactic discs. Mon. Not. R. Astron. Soc. 295, 319–336 (1998)

    ADS  Article  Google Scholar 

  5. 5

    Disney, M. J. in The Low Surface Brightness Universe (eds Davies, J. I., Impey, C. & Phillipps, S.) 9–18 (IAU Symp. 171, Astron. Soc. Pacif. Conf. Ser. 170, Astronomical Society of the Pacific, 1999)

    Google Scholar 

  6. 6

    Blumenthal, G. R., Faber, S. M., Primack, J. R. & Rees, M. J. Formation of galaxies and large-scale structure with cold dark matter. Nature 311, 517–525 (1984)

    CAS  ADS  Article  Google Scholar 

  7. 7

    Staveley-Smith, L. et al. The Parkes 21-cm multibeam receiver. Publ. Astron. Soc. Austral. 13, 243–248 (1996)

    ADS  Article  Google Scholar 

  8. 8

    Zwaan, M. A. et al. The HIPASS catalogue – II. Completeness, reliability, and parameter accuracy. Mon. Not. R. Astron. Soc. 350, 1210–1219 (2004)

    CAS  ADS  Article  Google Scholar 

  9. 9

    Meyer, M. J. et al. The HIPASS catalogue – I. Data presentation. Mon. Not. R. Astron. Soc. 350, 1195–1209 (2004)

    CAS  ADS  Article  Google Scholar 

  10. 10

    Adelman-McCarthy, J. K. et al. The fifth data release of the Sloan Digital Sky Survey. Astrophys. J. Suppl. Ser. 172, 634–644 (2007)

    ADS  Article  Google Scholar 

  11. 11

    Garcia-Appadoo, D. A., West, A. A., Dalcanton, J. J., Cortese, L. & Disney, M. J. Correlations among the properties of galaxies found in a blind HI survey. Mon. Not. R. Astron. Soc (submitted); preprint at 〈〉 (2008)

  12. 12

    Strateva, I. et al. Color separation of galaxy types in the Sloan Digital Sky Survey imaging data. Astron. J. 122, 1861–1874 (2001)

    CAS  ADS  Article  Google Scholar 

  13. 13

    Kulkarni, S. R. & Heiles, C. in Galactic and Extra-Galactic Radio Astronomy 2nd edn (eds Kellerman, K. I. & Verschuur, G. L.) 95–153 (Springer, 1988)

    Book  Google Scholar 

  14. 14

    Gavazzi, G., Pierini, D. & Boselli, A. The phenomenology of disk galaxies. Astron. Astrophys. 312, 397–408 (1996)

    CAS  ADS  Google Scholar 

  15. 15

    Blanton, M. R. et al. The galaxy luminosity function and luminosity density at redshift z = 0.1. Astrophys. J. 592, 819–838 (2003)

    ADS  Article  Google Scholar 

  16. 16

    van der Kruit, P. The three-dimensional distribution of light and mass in disks of spiral galaxies. Astron. Astrophys. 192, 117–127 (1988)

    ADS  Google Scholar 

  17. 17

    Haynes, M. P. & Giovanelli, R. Neutral hydrogen in isolated galaxies. IV – Results for the Arecibo sample. Astron. J. 89, 758–800 (1984)

    CAS  ADS  Article  Google Scholar 

  18. 18

    Rosenberg, J. L., Schneider, S. E. & Posson-Brown, J. Gas and stars in an HI-selected galaxy sample. Astrophys. J. 129, 1311–1330 (2005)

    CAS  ADS  Google Scholar 

  19. 19

    Jolliffe, I. T. Principal Component Analysis (Springer, 1986)

    Book  Google Scholar 

  20. 20

    Chatfield, C. & Collins, A. J. Introduction to Multivariate Analysis (Chapman & Hall, 1980)

    Book  Google Scholar 

  21. 21

    Kormendy, J. & Kennicutt, R. C. Secular evolution and the formation of pseudobulges in disk galaxies. Annu. Rev. Astron. Astrophys. 42, 603–683 (2004)

    ADS  Article  Google Scholar 

  22. 22

    Zibetti, S. et al. 1.65 micron (H band) surface photometry of galaxies. I. Structural and dynamical properties of elliptical galaxies. Astrophys. J. 579, 261–269 (2002)

    ADS  Article  Google Scholar 

  23. 23

    Conselice, C. J. The fundamental properties of galaxies and a new galaxy classification system. Mon. Not. R. Astron. Soc. 373, 1389–1408 (2006)

    ADS  Article  Google Scholar 

  24. 24

    Brosche, P. The manifold of galaxies. Galaxies with known dynamical parameters. Astron. Astrophys. 23, 259–268 (1973)

    ADS  Google Scholar 

  25. 25

    Balkowski, C. Statistical study of integral properties of galaxies measured in the 21-cm line. Astron. Astrophys. 29, 43–55 (1973)

    CAS  ADS  Google Scholar 

  26. 26

    Bujarrabal, V., Guibert, J. & Balkowski, C. Multidimensional statistical analysis of normal galaxies. Astron. Astrophys. 104, 1–9 (1981)

    ADS  Google Scholar 

  27. 27

    Shostak, G. S. Integral properties of late-type galaxies derived from HI observations. Astron. Astrophys. 68, 321–341 (1978)

    ADS  Google Scholar 

  28. 28

    Whitmore, B. C. An objective classification system for spiral galaxies. I. The two dominant dimensions. Astrophys. J. 278, 61–80 (1984)

    ADS  Article  Google Scholar 

  29. 29

    Dalcanton, J. J., Spergel, D. N., Gunn, J. E., Schmidt, M. & Schneider, D. P. The number density of low-surface brightness galaxies with 23 < μ0 25 V Mag/arcsec2 . Astron. J. 114, 635–654 (1997)

    CAS  ADS  Article  Google Scholar 

Download references


We would like to thank the HIPASS team, and especially R. Ekers, A. Wright and L. Staveley-Smith of the Australian National Telescope at CSIRO Radiophysics in Sydney for their foresight and enterprise in getting the Multibeam project started. M.J.D. would like to thank M. Disney of the Geography Department at University College London for first pointing out the one-dimensional nature of this data.

Author information



Corresponding author

Correspondence to M. J. Disney.

Supplementary information

Supplementary Information

This file contains a Supplementary Discussion and Supplementary Figures S1-S6 with Legends (PDF 1247 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Disney, M., Romano, J., Garcia–Appadoo, D. et al. Galaxies appear simpler than expected. Nature 455, 1082–1084 (2008).

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.


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