How the Edge of Our Galaxy Defies Known Physics

Dark Matter, the opposite action of physical things of friction. 
Also, opposite to the action of de-momentumizing through lame backward inertias.
Example a person is walking down the street and steps on gum. They slow, and see the gum but that didn't stop them, though a "type" of friction could mimic this action. The gum a molecular matter with geared bearings which turn backward to taunt force. Inertializing the whole substance to slow all things connected (grand scale), and also subjecting the whole mass to a lesser momentum.
This doesn't answer for Dark Matter, unless it gets 'benched' away from all the crazy momentums/inertias of outer space.