What is the composition of a quasar compared to a star or nebula?

Stars are born in nebulae, which are clouds of gas and dust primarily composed of hydrogen, with traces of helium and heavier elements and compounds.

A star is a ball of gas that is mostly hydrogen with a core that is hot enough and pressurized to support fusion reactions. Stars release heat and light.

A galaxy is a group of stars. The majority of galaxies have a supermassive black hole at their center. The region around young galaxies and galaxies that have collided with one another has a lot of gas and dust.

Near the supermassive black hole stars, dust and gas fall into the black hole, forming an accretion disk. As more and more material falls into the accretion disk, friction and gravity cause it to become superheated, and all of the energy is released as strong radiation beams, known as quasars.

Quasars are most likely to be young galaxies; the galactic nucleus stops being a quasar when material is removed from the region surrounding the supermassive black hole.

A star is primarily made up of hydrogen and helium, with trace amounts of heavier elements; a nebula is a cloud of gas and dust in space that is primarily made up of hydrogen and helium, with trace amounts of other elements. A quasar is primarily made up of superheated gas and dust surrounding a supermassive black hole at the center of a galaxy.