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.
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