Authors: Geoffrey M. Williams
A spiral galaxy is modeled as a thin, flat, axisymmetric disk comprising a series of concentric, coplanar rings. Using conventional Newtonian gravitation kinematics, it is shown that relatively flat velocity curves are produced by a variety of possible mass distributions in the disk. No halo of "dark matter" is needed to produce these rotation curves. Compared with a point mass at the center, the disk gravitational force grows with increasing distance from the disk center, crests and then slowly subsides beyond the disk perimeter. The model is applied to the NGC 3198, M31 and NGC 4736 galaxies, with ring masses adjusted to match the respective velocity profiles. Gravitational force fields in the disk are calculated, leading to direct estimates of enclosed galaxy mass. The mass distributions of several other spiral galaxies are analyzed, and their basic characteristics are charted in Appendix 2.
Comments: 29 pages.
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