What causes a quasar for form?
A quasar forms when material falls into the accretion disc around a supermassive black hole at the centre of a galaxy.
It has been observed that galaxies, including our own Milky Way galaxy, have a supermassive black hole at their centre. The supermassive black hole at the centre of our galaxy Sagittarius A* is about 4,000,000 times the mass of the sun. Other galaxies have much bigger black holes.
An accretion disc is a disc of material falling into a body such as a black hole. If material falls into the accretion disc around a supermassive black hole it gets heated by friction and gravitational effects to the point where it emits huge amounts of energy. This is a quasar.
The requirements for a quasar to form are a supermassive black hole at the centre of a galaxy with a lot of material falling into it. This typically occurs in young galaxies and when galaxies collide.
The quasars which have been observed are in young galaxies millions or billions of light years away. We see them as they were in the early universe.
In about 4 billion years time our galaxy will collide with the Andromeda galaxy. If the supermassive black holes at the centre of the galaxies combine there could be enough material available to form a quasar.