Question

How does the brightness of a quasar compared with that of a large galaxy?

Answer 1

The quasar 3C 273 has an apparent magnitude of about 12.8 whereas the brightest galaxy - the Large Magellanic Cloud has an apparent magnitude of 0.9. However, in absolute magnitudes, 3C 273 has an absolute magnitude of about -26.7 very similar to our own Sun.

Answer 2

The extraordinarily bright luminosity is generated by the ultraluminous nuclei, of a far distant galaxy.

Step-by-step explanation:
The fibrous quasar-fuzz reveals that the extraordinarily luminous star-like quasar is in a far distant galaxy. The point source of light called quasar is surmised as nuclei of the galaxy, appearing as a fuzz surrounding the quasar.

Luminosity of a quasar might be as large as 100000 times the luminosity of our galaxy Milky Way (MW). For a contrast: Sun;s luminosity L = 1 is about 1/(250 million) of MW luminosity.

What is observed as a quasar now is a revelation of what i was about billion(s) years ago.