  Physical mechanisms that can influence rotation curves of spiral galaxies are
discussed. For dark matter studies, possible contributions due to magnetic
fields and non-Newtonian gravitational accelerations should be carefully
accounted for. We point out that magnetic fields are particularly important in
outermost parts of the disk. In the framework of general relativity the
physical reason of an enhanced gravity in spiral galaxies depends on the
assumed metric. The additional gravity is provided for Schwarzschild metric by
nonluminous mass, whereas for Vaidya metric [1] by emission of radiative
energy. In the latter case the non-Newtonian acceleration displays 1/r
behaviour. Also matter flows contribute to non-Newtonian gravity.
