What fuel powers quasars?
A quasar is mainly fuelled by dust and gas.
Most galaxies have a supermassive black hole at their centres. Young galaxies and galaxies which have collided with another, often have large amounts of dust and gas at their centres.
The dust and gas start to fall into the black hole forming an accretion disc. As more and more gas and dust fall into the accretion disc they heat up due to friction and gravity.
Very hot material has very high energy particles and give off radiation. The magnetic field of the block hole causes radiation to be emitted in jets. The jets are very powerful and can contain the whole spectrum from radio waves to gamma waves.
So quasars are mainly powered by dust and gas. It is possible for other bodies, including stars, to get torn apart by gravity and add to the fuel supply.