What is the main evidence that we have that the luminous central region of a quasar is small and compact? What is the main evidence that we have that the luminous central region of a quasar is small and compact? The central region of quasars can be observed directly by the Hubble space telescope. Fluctuations in the energy output of a quasar can change over relatively short time periods (a few months to a few years at most). The central region emits extra high energy neutrinos that vary overtime. or Fluctuations in the measured redshift of a quasar can change over relatively short time periods (a few months to a few years at most)