Quasars are the glowing part of distant galaxies; they achieve this by emitting electromagnetic radiations of very high frequencies detectable as bright light.
According to Einstein’s energy equation E=MC2, an object emitting high energy will continuously reduce its mass as it discharges more energy and will cease to be matter as it attains the speed of light. Due to the high frequency of visible light, quasars have to be relatively small to be capable of emitting visible light.
The extent of quasars dimensions is a few light hours. This fact is elaborated by Breithaupt. Soon after quasars were discovered, astronomers detected fluctuations in brightness over time as short as a few hours. Those rapid fluctuations show quasars are small objects, not more than a few light-hours in diameter.