When we look at galaxies they appear to be rotating at such a speed that they should rip themselves apart. One of the leading explanations for why they don't is that there is a large amount of Dark Matter which we can't see that forms the gravitational glue holding galaxies together. Another explanation is MOND (Modified Newtonian Dynamics) which posits that for very low accelerations Newton's Second Law of Motion (f=ma) does not hold and the acceleration is disproportionately large. Hence at extreme distances the acceleration due to gravity is larger than one would expect

This is a very rough (given the need to make it run fast and also my lack of interest in spending the time required to simulate anything too closely) demonstration of the MOND concept operating in a restricted 2 dimensional plane. I'm not endorsing MOND by using a bastardised form of it for this simulation. I really wouldn't know. Its just much easier to implement and much faster to simulate than dark matter.

Note that if you don't move the mouse staring at this simulation for any period of time and then looking away will lead to the illusion that the area at the centre of your vision is rotating in the opposite direction. This effect, while mildly disconcerting, is short lived. Any lingering disruption to the senses is down to that red pill you just swallowed.