I’m pretty sure that one piece of evidence for dark matter is that galaxies with dark matter have flat rotation curves. This means as you move outwards from the

I’m pretty sure that one piece of evidence for dark matter is that galaxies with dark matter have flat rotation curves. This means as you move outwards from the centre of the galaxy, it turns out counterintuitively that objects have the same orbital speed. Because of Kepler’s laws, this implies that each farther orbit is encompassing more and more mass to give the farther object the same speed as the inner ones. Dark matter is spread out through the whole galaxy extending far out past the luminous matter like stars. If this mass was all in the centre inside the event horizon like you’re saying, the rotation curve of the galaxy would not be flat. The orbital speeds would drop off like they do in our solar system.