Title : Correct accounting of gas kinetics in disks of spiral galaxies, explains non-Keplerian rotation curves and makes dark matter unnecessary
Until now, it was generally accepted that the gas kinetics is not important in the formation of rotation curves (RC) of spiral galaxies (see Dalcanton and Stilp, doi:10.1088/0004-637X/721/1/547). For this reason, RC is usually calculated within the framework of a naive Newtonian mechanical model, adding dark matter to the model to fit the calculated RC to the observed one. Thus, non-Keplerian RCs are commonly calculated as Keplerian ones, but with the addition of about 90% of the mass in the form of dark matter. In this paper, it is shown that the commonly used methods of classical mechanics cannot be used to calculate RCs in the outer parts of galactic disks, where the influence of collisions in the gas on its dynamics becomes dominant. Moreover, the hydrodynamic approach also cannot be applied for these purposes, due to the extreme rarefaction of the gas in the galactic disks. It is argued that gas kinetics plays a key role in the dynamics of gas in the outer parts of galactic disks, for which non-Keplerian RCs are observed.
In this work (see Lipovka doi: 10.31219/osf.io/t6754 ), we have developed a new method for describing the dynamics of a rarefied gas in the outer regions of galactic disks, where the gas dynamics is mainly determined by collisions. In this paper, equations describing RC are derived. In this case, the obtained equations are free from restrictions imposed on hydrodynamics. The resulting equations relate two quantities: the tangential gas velocity as a function of the distance from the galactic center (RC) and the radial gas density distribution. It is shown that if the physical properties of a rarefied gas are taken into account correctly, there is no need to introduce dark matter. In this case, the "non-physical" (not Keplerian) rotation curves for the outer parts of galaxies are tailwinds described in the framework of the usual kinetic theory of gas. To illustrate the correctness of the model obtained, two galaxies with flat rotation curves (NGC7331 and NGC3198) are considered. Excellent agreement was obtained between the densities calculated from the rotation curve and the observed values, which confirms the correctness of the model used. Thus, the “nonphysical” rotation curves of spiral galaxies, which previously required dark matter to explain, are just tailwinds formed in a rarefied gas. Therefore, their explanation does not require the involvement of the concept of dark matter. The total masses of the galaxies NGC7331 and NGC3198 have been calculated. The implications for cosmology are discussed.