Sure you hear about this stuff, but what is it and what’s the problem? I heard on a podcast a simple explanation! As we look at our galaxy we know it spins… But what we don’t know is why it doesn’t fling stars out of the edges as it spins ( like the force you feel on a merry go round). You might imagine the force pushing stars away from the center which is what newton observed and explained. The concept of the “dark” matter is that to hold the stars in the galaxy, there must be more things with gravity that we cannot see. More stuff, more matter. Since we cannot see it, its referred to as “dark”. The idea is being debated with suggestions that newton was wrong for slow forces ( the F in f=ma). Maybe we will find out in our lifetime what the answer is. I certainly hope so as it appears most of the matter is “missing”.

Our current models of the universe actually requires the presence of Energy and Matter which we cannot find as shown in this pie chart.

Dark Matter Pie Chart