When astronomers first started using radio telescopes in the 1950s to study the Universe, they discovered a strange phenomenon. They found objects that shone brightly in the radio spectrum, but they couldn’t see any visible object associated with them. They called them quasi-stellar radio sources, or “quasars” for short.
Within a decade of their discovery, astronomers learned that these quasars were moving away at tremendous velocities. This velocity, or red-shift of their light, indicated that they were billions of light-years away; beyond the capabilities of most optical telescopes. It wasn’t until the 1960s when a quasar was finally tied to an optical object, a distant galaxy.
Since then, thousands of quasars have been discovered, but astronomers had no idea what they were. Finally in the 1980s, astronomers developed unified models that identified quasars as active galaxies. The bright radiation coming from them is because of the accretion disks surrounding the supermassive black holes at their centers. We see a quasar when a supermassive black hole is actively feeding on the surrounding material.
Since our own Milky Way has a supermassive black hole, it’s likely that we have gone through many active stages, whenever material is falling into the black hole; our galaxy would be seen as a quasar. But other times, like now, the supermassive black hole is quiet.
With new powerful telescopes, astronomers have observed that some quasars have long jets of material firing out from the center of the galaxy. These are channeled by the magnetic fields created by the supermassive black hole’s rotation in the accretion disk. The most luminous quasars can exceed the radiation output of an average quasar.
We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.