When matter falls into a supermassive black hole's accretion disc.

How are quasars formed?


Explanation

The centers of most galaxies are expected to contain supermassive black holes. These black holes feature accretion discs, which are made up of material that spirals into the black hole.

When material falls into the accretion disc, friction and gravitational forces heat it up. The enormous output of a quasar is caused by the energy generated by this.

Read More — What Is A Quasar?

When a supermassive black hole at the center of a galaxy has enough material surrounding it to fall into the accretion disc and provide enough energy to fuel it, a quasar is formed.

Young galaxies and colliding galaxies are the only galaxies with enough material to form a quasar. Unless they collide, all neighboring galaxies are too old to be quasars. Quasars are extremely distant galaxies whose light has taken billions of years to reach us. We are witnessing young galaxies, much like the Universe was when it was young.

Our own Milky Way galaxy was most likely a quasar in its youth, with a lot of material pouring towards the core black hole. When it collides with the Andromeda galaxy in around 4 billion years, it may re-emerge as a quasar.

Read More — Scientists showed how the earliest quasars formed