Your second reading in this section is the Cambridge University education page on active galactic nuclei. These galaxies are special in that the supermassive objects in their cores are actively feeding on infalling material. The feeding causes these incredibly massive objects to be anything but black!
Our third reading assignment in this section is an education page from Swinburne University that describes these brightly emitting supermassive black holes in greater detail. Pay close attention to why we can see light at all from an object that has such a strong gravitational field that not even something traveling with speed "c" can escape! Also look at the possible explanation of the jets of material that the AGNs are often associated with.
Our final reading assignment is an education page from NASA's Imagine the Universe that covers AGN and quasars. By the end you should see how we believe quasars and AGN are related to each other!