Quasars are huge, energetic, mysterious objects in space. Modern technology has allowed humans to understand these objects better.
Quasars create a massive amount of light, allowing them to be seen from great distances. The farthest quasar from Earth is located 12 billion light years away in the middle of young galaxies. At the center of a quasar is a huge, spinning black hole. The black hole creates massive amounts of energy. It’s so massive that the average size of a black hole can be one billion times larger than the sun!
Where does this energy come from? In order to obtain energy, the black hole takes in stars, gas and dust from a cauldron of swirling gas called an accretion disc, which surrounds the black hole. As the accretion disc spins around the black hole, the stars, gas and dust become compressed and by spinning around, energy is created in the form of heat. The millions of degrees of heat become the black hole's food. Sooner or later, the violent process begins to create a cavity on the accretion disc.
Finally, the disc cuts off the food supply to the black hole and it loses energy. This means it can’t continue producing light. Quasars stay in this hiatus until they bump into a new energy source.
When the quasar is starved of energy over billions of years, the quasar's galaxy becomes peaceful, and normalized, similar to the galaxies closer to the Earth.
[Source: Visions of the Universe]