Hey all, got a question.

I saw a documentary about dark matter. It stated that Vera Rubin found that the stars on the edge of a spiral galaxy move at the same speed as the stars in the center. Also known as the Galaxy Rotation Problem.

BUT scientists have proved that there is a super massive black hole in the center of our galaxy by measuring the immense speed of the stars in the center.

So which is it?

SoBe8503: "So which is it?"

It's both (probably). Whether the matter at the center is in the form of a black hole or millions of stars makes no difference to the orbital velocity of the outlying stars. The gravity would be the same either way. On the other hand, for those stars very close to the black hole I would think the effect of the dark matter ~50,000 lt.yrs. away, beyond the galactic rim, would be a very minor factor by comparison.

It's a good question, and I guess it really warrants a mathematical answer, but not from me I'm afraid

A few (supposedly equivalent) explanations of Galaxy Rotation Problem you can find here. It's basically a product of omnidirectional Universe expansion in connection to general relativity.