Why do we think that active galaxies have small core regions?
A) We can measure their size on the sky, which means they are small and near.
B) They emit radio waves that larger objects cannot do.
C) Their light varies rapidly, implying small radius.
D) They are very far away, and thus are younger and less expanded.

Question

Quizplus · Accepted Answer

The rapid variability in the light emitted by active galaxies suggests that the emitting region is small, as changes in brightness occur over short timescales, indicating a compact core.

Why Do We Think That Active Galaxies Have Small Core