Here is a paper that discusses a possibility that the General Relativity alone can be enough to explain the observed dynamics of galaxies:

https://arxiv.org/abs/0712.0019

From the paper:

we are witnessing here the power of the nonlinearities inherent in general relativity in the context of weak gravity to effect very significant changes relative to the results expected on the basis of Newtonian theory. It suggests that hitherto unexplained astrophysical phenomena be re-considered on the basis of the application of general relativity to weak-field gravity.