All galaxies contain supermassive black holes at their centers that have a mass one million times greater than the Sun. Many of these black holes sit there quiescently, but some cause quite a bit of fuss. Galaxies with these latter types of black holes are known as active galaxies or active galactic nuclei (AGN). The black holes in AGN have large amounts of dense gas swirling into them via an accretion disk, which heats up an emits light that affects surrounding gas clouds. Strong magnetic fields also play a large role in the light that hits clouds in the vicinity in the black hole.
As AGN start to settle down, their brightness decreases to point that they look like a typical star forming or elliptical galaxy. The physical processes that occur in order for this happen are not well understoood. One idea is that the clouds surrounding the black hole get pushed so far away by radiation, that the light from accretion disk no longer has any influence on them. Below, I've outlined a few of the broader questions that our group is interested in investigating.