Ive been watching a video about dark mater and Joe al lot of the mass is missing in our universe. And astronomers got to this by measuring the speed that stars orbit he Center of the galaxy and when they did this I didn't match the amount of gravity/mass in the galaxy.
However I thought that the mass of the black hole in the Center of the galaxy was measured by the stars orbiting it? To me it sounds like a catch 22? But I dot understand it very well. So could someone explain it further?