Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981ap%26ss..74..391b&link_type=abstract
Astrophysics and Space Science, vol. 74, no. 2, Feb. 1981, 391-407.
Astronomy and Astrophysics
Astrophysics
3
Disk Galaxies, Galactic Nuclei, Gas Flow, Interstellar Gas, Magnetohydrodynamic Flow, Radial Flow, Deposition, Flow Equations, Flow Velocity, Magnetization, Rotating Fluids, Stellar Mass Ejection, Viscous Flow
Scientific paper
In a previous paper (hereafter referred to as Paper I) we have tried to show that superdense cores in the nuclei of disk galaxies can be formed by accretion of gas ejected by the evolved stars which populate the central bulge of these galaxies. Solving the equations for radial flow of a magnetized gas, we found that the accretion of an explodable mass at the core can be achieved over a time-scale ranging from a few times iO~ and a few times 108 yr. It was shown, however, that the accretion process is seriously inhibited if the gas possesses sufficient rotational velocity but lacks any dissipative mechanism within the system. Since rotational velocity is an observed parameter of the stars which shed the gas to be accreted, one must consider the existence of some dissipative force in it in order that the accretion process may be efficient. In the present paper, therefore, we have solved the problem of the flow of a rotating, viscous (variable), magnetized gas. With plausible assumptions regarding some of the parameters involved, the time-scale for the accretion of an explodable mass (~- i09 M®) at the core again turns out to be ranging between a few times iÃ&~cedil; and a few times 108 yr. Such time-scale has been proposed by several authors as that for repeated explosions in nuclei of these galaxies. It has also been proposed by many authors that the spiral arms are generated and destroyed in disk galaxies over the same time-scale. Our solution also yields a nearly linear rotational velocity law which is usually observed in the central regions of these galaxies
Basu Baidyanath
Bhattacharya Tanmoy
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