Quasars are difficult to study because they are the active nuclei of distant galaxies.
The microquasar black hole systems, however, are within our own the Milky Way galaxy, only 10,000 and 40,000 light years from Earth. These microquasar systems have a normal star orbiting a black hole. Material being pulled from the star into the black hole forms an accretion disk around the black hole. Scientists knew these systems also have a 'hot' corona, a cloud of plasma and gas surrounding the black hole. There were a couple of competing theories.