The Spiral Structure of Galaxies
About two-thirds of all galaxies are spiral galaxies, and a large number of them, more than two-thirds, have a regular spiral structure with two arms that can be followed continuously from the centre of the galaxy (the central bulge) to the extremities of the disc. This structure has for a long time posed a serious theoretical problem concerning its origin and persistence in galaxies. The density-wave theory and the amplification mechanism of these waves provide a beautiful solution to the problem in the majority of cases. Before going into the details of this theory (in Section 5.2), we must first tackle the problem of the gravitational stability of a galactic disc and define the main characteristics of the orbits of stars in a rotating disc (the theory of epicycles).
Unable to display preview. Download preview PDF.
- Arp, H. (1966) Atlas of Peculiar Galaxies (California Institute of Technology, Pasadena CA).Google Scholar
- Baade, W. (1963) in Evolution of Stars and Galaxies, edited by C. Payne-Gaposchkin ( Harvard University Press, Cambridge MA).Google Scholar
- Binney, J., and Tremaine, S. (1987) in Galactic Dynamics ( Princeton University Press, Princeton NJ).Google Scholar
- Sandage, A. R. (1961) The Hubble Atlas of Galaxies ( Carnegie Institution of Washington, Washington DC).Google Scholar
- Schmidt, M. (1965) in Galactic Structure, edited by A. Blauw and M. Schmidt ( University of Chicago Press, Chicago IL ), p. 513.Google Scholar
- Toomre, A. (1981) in The Structure and Evolution of Normal Galaxies, edited by S. M. Fall and D. Lynden-Bell ( Cambridge University Press, Cambridge).Google Scholar
- Zang, T. (1981) quoted in Toomre (1981).Google Scholar