Final answer:
Quasars are thought to be relatively small in size because they emit a tremendous amount of power from a small region. The fluctuations and rapid variability observed in quasars indicate that the energy-generating region must be small.
Step-by-step explanation:
Quasars are thought to be relatively small in size because they emit a tremendous amount of power from a small region. The fluctuations and rapid variability observed in quasars indicate that the energy-generating region must be small. For example, the X-ray band observations show that the more energetic radiation is generated in an even smaller region. This suggests that the mass around which the accretion disk is swirling must be confined to a space that is even smaller.