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Radial Motions Near the Galactic Centre and the Origin of Galactic Spiral Structure

Published online by Cambridge University Press:  12 April 2016

Th. Schmidt-Kaler
Th. Schmidt-Kaler*
Affiliation:
Astronomisches Institut der Ruhr-Universitãt Bochum

Extract

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The fundamental difficulty of explaining the spiral structure of galaxies by material arms is the winding dilemma which restricts the life-time of a spiral to about one rotation period. This dilemma is resolved by the density wave concept. However, the density waves are damped by various processes. We calculated the life time of the density wave for our Galaxy (τ = 8.108 yrs) as well as for 24 nearby spiral galaxies with well-known data. It appears that the density wave can explain the existence of spiral arms for only about three rotation periods. After that time the energy of the wave has to be re-supplied. For this, various mechanisms have been proposed, e.g.

  • 1) tidal origin – which requires rather special circumstances

  • 2) resonant interaction – which is energetically insufficient

  • 3) local Jeans-type instability in the outer regions – which also may not be able to provide sufficient energy

  • 4) explosions of the nucleus – which involve high inclinations to the plane.

Type
Part II: Evolution of the Central Parts of the Galaxy
Information
International Astronomical Union Colloquium , Volume 45: Chemical and Dynamical Evolution of our Galaxy , September 1977 , pp. 125 - 129
Copyright
Copyright © Geneva Observatory 1977

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