Gas kinetics of galactic disk explains rotation curves of S-type galaxies without a need for Dark Matter.

Abstract

In the paper a way to explain Rotation Curves (RC) of galaxies without involving Dark Matter (DM) concept is suggested. It was done by including into our model physical properties of a rarefied gas, which was not taken into account earlier. It is shown that the observed non-Keplerian rotation curves of the outer parts of galactic disks appear in the case of gas densities of more than 10 (-5) cm(-3) and can be explained as tailwinds.We prove, that generally used methods of classical mechanics cannot be applied to calculate RCs of spiral galaxies. Moreover, the equations of hydrodynamics are also not applicable for this purpose due to the extremely rarefaction of gas in galactic disks.Starting with the kinetic equations, we got a Modified diffusion Equation (MDE), which describes motion of the rarefied gas in galactic disks. We show, that the observed non-Keplerian RCs observed for outer part of disks, and the measured radial gas distribution are closely related by obtained MDE. Thus, if the description of the rarefied gas dynamics is made correctly, then DM is not required to explain the rotation curves of galaxies. It is stressed, that while the inner part of the RC is subject of the Kepler law, for the correct description of the outer part of the RC, the collisional property of the gas should also be taken into account.To illustrate the validity of the obtained equation (13), we consider two galaxies (NGC7331 and NGC3198) characterized by flat RCs. An excellent coincidence between the measured column density of gas and that calculated from observed RCs is obtained.Total masses of NGC7331 and NGC3198 are calculated. Consequences for cosmology are discussed.