The center of the Milky Way was an active galactic nucleus in the past.What direct observational evidence supports this?

Question

Quizplus · Accepted Answer

All three choices provide evidence that the center of the Milky Way was an active galactic nucleus in the past. 
A) Gamma-ray bubbles indicate the presence of past galactic activity that produced high-energy particles. 
B) The rapid motions of stars near the galactic center suggest the presence of a massive object, such as a black hole, which could have been actively feeding in the past. 
C) X-ray emission near the galactic center also indicates the presence of hot gas and high-energy activity, consistent with an active galactic nucleus.

The Center of the Milky Way Was an Active Galactic