Letter | Published:

A dynamical instability of bars in disk galaxies

Naturevolume 352pages411412 (1991) | Download Citation



STRONG, rapidly rotating, persistent bars readily form in numerical simulations of initially axisymmetric disk galaxies1–4. The global dynamical instability responsible for this behaviour is a great embarrassment to the subject of galactic dynamics, as most galaxies in the sky do not possess a strong bar5; the suggestion3 that the dark matter content of galaxies might resolve this discrepancy is unattractive6. Here we present the results of three-dimensional simulations which show that the bar is dynamically unstable to buckling out of the galactic plane (the majority of previous disk galaxy simulations have been strictly two-dimensional). Stars acquire large motions normal to the plane, giving the bar a peanut shape through a mechanism that we suggest to be the fire-hose instability7–9. Bars may be weakened or even destroyed by this instability; thus the fraction of disk galaxies containing strong bars today could be lower than the fraction in which they have formed in the past. The instability may also account for the peanut morphology of many galaxies, and because it leads to a less flattened stellar system with increased central density, it may play a part in the formation of galactic bulges.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1

    Miller, R. H. & Prendergast, K. H. Astrophys. J. 151, 699–709 (1968).

  2. 2

    Hockney, R. W. & Hohl, F. Astr. J. 74, 1102–1104 (1969).

  3. 3

    Ostriker, J. P. & Peebles, P. J. E. Astrophys. J. 186, 467–480 (1973).

  4. 4

    Efstathiou, G., Lake, G. & Negroponte, J. Mon. Not. R. astr. Soc. 199, 1069–1088 (1982).

  5. 5

    Sandage, A. & Tamman, G. A. A Revised Shapley-Ames Catalog of Bright Galaxies (Carnegie Institution of Washington, 1981).

  6. 6

    Kalnajs, A. J. Dark Matter in the Universe, IAU Symp. No. 117 (eds Kormendy, J. & Knapp, G. R.) 289–296 (Reidel, Dordrecht, 1987).

  7. 7

    Toomre, A. Geophysical Fluid Dynamics, Notes on 1966 Summer Study Prog. Woods Hole Oceanographic Institution. No. 66-46, 111–114 (1966).

  8. 8

    Araki, S. thesis, Massachusetts institute of Technology (1985).

  9. 9

    Jarvis, B. J. & Freeman, K. C. Astrophys. J. 295, 314–323 (1985).

  10. 10

    Toomre, A. Astrophys. J. 138, 385–392 (1963).

  11. 11

    Toomre, A. Astrophys. J. 139, 1217–1238 (1964).

  12. 12

    James, R. A. J. comput. Phys. 25, 71–93 (1977).

  13. 13

    May, A. & James, R. A. Mon. Not. R. astr. Soc. 206, 691–701 (1984).

  14. 14

    Hernquist, L. Astrophys. J. suppl. Ser. 64, 715–734 (1987).

  15. 15

    Fridman, A. M. & Polyachenko, V. L. Physics of Gravitating Systems (Springer, New York, 1984).

  16. 16

    Merritt, D. & Hernquist, L. Astrophys. J. (in the press).

  17. 17

    Combes, F., Debbasch, F., Friedli, D. & Pfenniger, D. Astr. Astrophys. 233, 82–95 (1990).

  18. 18

    Friedli, D. & Pfenniger, D. in Bulges of Galaxies, Proc. ESO Workshop, No. 35 (eds Jarvis, B, J. & Terndrup, D. M.) 265–268 (ESO, 1990).

  19. 19

    Shaw, M. A. Mon. Not. R. astr. Soc. 229, 691–706 (1987).

Download references

Author information


  1. Department of Astronomy, The University, Manchester, M13 9PL, UK

    • N. Raha
    • , J. A. Sellwood
    • , R. A. James
    •  & F. D. Kahn


  1. Search for N. Raha in:

  2. Search for J. A. Sellwood in:

  3. Search for R. A. James in:

  4. Search for F. D. Kahn in:

About this article

Publication history



Issue Date



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.