Modified Newtonian Dynamics
Modified Newtonian dynamics (MOND) is very good at explaining the rotational curves of spiral galaxies that are in equilibrium (i.e. ones which haven't undergone any recent mergers). Analysing MOND using generalized dark fluid equations, one finds that where MOND falls short is in merging systems like galactic clusters, where time-dependent equations are important, but MOND doesn't take these into account adequately. The MOND theory is actually the dark fluid theory's static special case when galaxy structures are in equilibrium. It is estimated that the average time for oscillations inside a galaxy to settle down after a disturbance event is about 1 Gyr ( years, one giga-year), at which point it begins to match MOND. Interestingly, dark fluid predicts that due to time-dependent variables, the current universe is not old enough for all galaxies to conform to MOND yet, but that after about 100 Gyr, the galaxies in the universe would mostly resemble MOND.
Read more about this topic: Dark Fluid
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