Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976ap%26ss..44...47c&link_type=abstract
Astrophysics and Space Science, vol. 44, Sept. 1976, p. 47-62.
Astronomy and Astrophysics
Astronomy
4
Cosmology, Galactic Evolution, Galactic Structure, Milky Way Galaxy, Spiral Galaxies, Stellar Motions, Expansion, Galactic Nuclei, Hydrogen, Radio Astronomy, Seyfert Galaxies, Stellar Mass Ejection
Scientific paper
The paper attempts to establish a kinematic description of the Galaxy without appealing to dynamical principles. Considerable emphasis is placed on the assumption of galactic 'spatiokinematic bisymmetry', which is justified by the frequent occurrence of double structure on the galactic scale. Evidence derived from stellar proper motions and radio observations of neutral hydrogen and molecular clouds is reviewed which indicates that the Galaxy is expanding in such a way that material at the center moves faster than material further out. Neutral-hydrogen observations in the galactic plane are analyzed to demonstrate that the data obtained may be interpreted as arising from an expanding two-arm spiral. It is shown that: (1) the spiral arms of the Galaxy can be followed more or less continuously through about six revolutions; (2) mass ejection from the galactic nucleus has continued for about the last 5 million years at a rate of some 10 solar masses per year; and (3) the phenomenon in the galactic center which caused this outflow may be most readily likened to the relatively short-lived processes occurring in the nuclei of Seyfert galaxies. It is suggested that the expanding spiral structure is formed by bursts of matter ejected over a short period from a bisymmetrical rotating source in the galactic nucleus.
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