April 06, 2015
This is the second paper dedicated to detailed calculations of disk galaxies. The first is “On orbital velocities in disk galaxies : “Dark Matter”, a myth?”  wherein I explain how to calculate the mass distribution of a disk galaxy and the orbital velocities of the stars, starting from a mass distribution of the originally spherical galaxy. This is based on the extended gravitation theory, called “Gyro-Gravitation” or gravitomagnetism. No existence of Dark Matter nor any other fancy supposition is needed at all in these calculations.
The objective of this paper is to find the mathematical equations related to the time which is needed for the star's orbit to swivel down to the equator. The total diameter-change of the disk galaxy in the time can be found as well. Yet, these deductions are simplified by keeping constant the bulge's gyrogravitational properties during the process. I leave to the reader to experiment with time-dependent models of gyrogravitational fields in the bulge.
An explanation for the very limited windings of our Milky Way's spirals is a direct consequence of this paper.