The Gamma Ray Universe
As the LAT scanned the cosmos, it quickly found a universe filled with active galaxies—galaxies that emit huge jets of radiation from their cores. Most of this is gamma ray radiation and so had not been seen before.
Astronomers had identified three types of active galaxies—Seyferts, Quasars and Blazars. Seyferts emit low energy gamma rays up to about 100 kilo electron Volts (keV)—one eV is the energy gained by an electron accelerated through a potential of one volt.
Quasars are extremely bright galaxies very far away—perhaps 12 billion lys distant or more. They also emit copious levels of gamma rays, 100 MeV and more, some up to several TeV.
Blazers are the gamma ray champs however, matching and exceeding Quasars. They are closer, but exhibit some strange behavior. Both in gamma ray emission and in visible light, they are variable, their emissions varying over days or weeks. Astronomers have not been able to explain this phenomenon yet.
All three types of active galaxies are thought to be the same. It just depends on how we are looking at them. If the jet is pointed directly at the Earth, we see an intense high energy beam. If we are looking at the beam from the side, we see only a low intensity source—a Seyfert.