How do quasars differ from galaxies?
A quasar is the center of a far distant galaxy, that has an extremely bright center.
Perhaps, a quasar is the Black Hole of a galaxy, from which light
might break out, from the edges.
Perhaps, the circular glow, with several-light years-wide dark region
across, from that great distance, is viewed as a a point source of
very bright light..
The energy emitted by a quasar might exceed the total of energies
of all stars of the galaxy of which the quasar is a point source of
extreme radiation, at the center.