Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976ap%26ss..45..243h&link_type=abstract
Astrophysics and Space Science, vol. 45, Nov. 1976, p. 243-248.
Astronomy and Astrophysics
Astrophysics
1
Astronomical Models, Astrophysics, Dynamic Stability, Spiral Galaxies, Gravitation Theory, Kinetic Energy, Stellar Evolution, Stellar Motions, Velocity Distribution
Scientific paper
Physical arguments suggest the spiral arms may be manifestations of the galaxy not being in dynamical equilibrium, in the sense that the kinetic energy of its stars and gas is less relative to its binding energy than that dictated by the virial theorem. Without constant cooling of the galactic disk, such a departure from dynamical equilibrium would be corrected and the spiral arms destroyed in about one billion years due to an increase in the velocity dispersion of the stars in the disk resulting from their interacting with the spiral arms. The rate of cooling required to maintain the spiral arms, may be provided by mass loss from stars in the disk population. The cooling arises from the average scale-heights and velocities of these stars being larger than that of the gas in the disk, so that there is a net loss of kinetic energy and an increase in the binding energy of the galaxy due to the ejected gas settling down to a lower terminal velocity and scale-height in the galactic disk.
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