The hypothesis of dark matter originates from the galaxy rotation problem which is a discrepancy between the predicted angular motion of galaxies near its edge and the observed motion by galactic rotation curves. The stuff at the edges was found to be moving just as fast as the stuff near the centre, apparently violating Newton's Laws of Motion which explains the motion of planets around the Sun. The conclusion was that most galaxies must contain about 6 times as much dark mass as visible mass.
However, it was subsequently discovered that the interstellar medium of Messier 64 (Black Eye Galaxy) consists of 2 counter-rotating disks that are approximately equal. Also, NGC 4550 (a galaxy in the Virgo Cluster) has a strange property that its stars seem to rotate in opposite directions. Movements of objects in the galaxy are not elliptical like planets around the Sun in the Solar System but fundamentally different spiral like a cyclone/hurricane/typhoon.
The evidence of gravitational lensing is attributed to dark matter, but the lensing effect can be explained by the existence of a black hole between the object and the Earth.
Observation of planet Jupiter's Red Spot (a rotating high pressure system) reveals that the stuff at the edges is found to be moving just as fast as the stuff near the centre.
In electromagnetism, Maxwell's equations are shown to be approximations. Some special situations can be noticeably inaccurate, i.e., extremely strong field, extremely short distances, non-classical light, quantum entanglement of electromagnetic fields, etc.
In electromagnetic radiation, far-field E and B field strength decreases inversely with distance from the source, resulting in an inverse-square law for the radiated power intensity. By contrast, near-field E and B strength decreases more rapidly with distance.
Cornstarch dissolved in dihydrogen monoxide (H2O) is a Shear Thickening Non-Newtonian fluid which does not follow Newton's Law of Viscosity. The viscosity of a shear thickening fluid (dilatant fluid) appears to increase when the shear rate increases. When cornstarch dissolved H2O is stirred slowly it looks milky, when cornstarch dissolved in H2O is stirred vigorously it feels like a very viscous liquid.
Therefore, a spiral galaxy populated with primordial black holes could behave like cornstarch dissolved in H2O, exhibiting its rotation in which the stuff at the edges is found to be moving just as fast as the stuff near the centre just like Jupiter's Red Spot, as well as gravitational lensing by the numerous black holes in the galaxy. Some black holes are remnants of super-massive black holes at the centre of other galaxies that had merged previously. This explanation without dark matter is analogous to gravitational far-field (1 / (d ^ 1)) versus gravitational near-field (1 / (d ^ 2)).
My understanding of the movement of a galaxy is that it is simulated with Newtonian physics because Relativistic calculations would far-exceed the capabilities of today's super-computers. If Relativistic calculations in the movement of galaxy become possible, then surprising results could emerge, impacting the nature of so-called Dark Matter.
Yet another factor to explain the Dark-Matter behaviour of galaxies is a web of magnetic attraction forces due to an inverse-square law among neutron stars including magnetars.
