Another explaination of an active galaxies bright center is that it is even a black hole. These black holes give energy to the rise of the quasars and active galactic nuclei. The black hole captures the large amount of matter that becomes congested near the accretion disk. When the gases and such spiral towar the middle the release large amounts of energy, in turn giving the center it's bright luminosity. The four forces in the physical universe are Gravity, electromagnetic force, and strong and weak nuclear force.
Gravity is the weakest of all four forces but unlike the others it has an unlimited range.
And this is why it is the one that shapes the universe. The more the masses, the greater the force, and an example of this would be our own solar system. Keeping them in thier positions over a large area of space is a perfect example of how this force works. The electromagnetic force has a repulsive element as well as an attractive one. And finally the weak nuclear force is said to be so weak that it does not hole anything together.