How do astronomers know that the luminous regions of active nuclei of active galaxies are very small
A)Their nuclei are much brighter than expected.
B)The orbits of stars near the center of the galactic nuclei are faster than expected.
C)The luminosity of the nuclei varies over short times.
D)The color of the nuclei is different than expected.

Question

Quizplus · Accepted Answer

The luminosity of the nuclei varies over short timescales, indicating that the region producing the light must be relatively small, as larger regions would take longer to change brightness significantly. This rapid variability is a key piece of evidence for the compact size of the luminous regions in active galactic nuclei.

How Do Astronomers Know That the Luminous Regions of Active