Problems of the Galaxies

Galaxies are observed to spin as if they were solid disks, but according to theory, the center of the galaxy should be spinning much faster than the edges. In order to explain the rotation of galaxies they need the entire galaxy filled with some kind of substance which holds the stars strongly together.

See http://news.softpedia.com/news/Stars-escaping-out-of-the-Galaxy-17222.shtml

"According to theory, a galaxy should rotate faster at the center than at the edges. This is similar to how an ice-skater rotates: when she extends her arms she moves more slowly, when she either extends her arms above her head or keeps them close to the body she starts to rotate more rapidly. Taking into consideration how gravitation connects the stars in the galaxy the predicted result is that average orbital speed of a star at a specified distance away from the center would decrease inversely with the square root of the radius of the orbit (the dashed line, A, in figure below). However observations show that the galaxy rotates as if it is a solid disk as if stars are much more strongly connected to each other (the solid line, B, in the figure below)."