A roulette wheel and dark magic
In my blog "On a rubber mat" I briefly described how space-time is determined by its mass energy contents. For instance, a star curves the space around it creating a gravitational pot hole where other matter falls and gets imprisoned. The bigger is the mass the more curvature is resulted. In a galaxy there are billions of starts each contributing to the total curvature of the space around the galaxy. Stars have motion that prevents them to fall in to the center of galaxy. In the center of a galaxy there is likely always a super massive black hole. You can think a roulette where you throw multiple balls that start spinning around the center. In contrast to the roulette wheel, there's no friction in the space reducing the speed of the stars, which lets them to orbit the center for ages. If we were able to add more enough speed to a ball while spinning, it would eventually reach the edge of the wheel and rolls out with its current direction. If a star had high enough veloc