Why do almost all active galaxies occur in clusters of galaxies? ...

[BRWH]

Why do almost all active galaxies occur in clusters of galaxies?
 
  What will be an ideal response?

Question 2

The lunar mare are radioactively dated at:
 
  A) 4.6 billion years old, forming first among the lunar features.
  B) 4.2-3.9 billion years old, comparable to the adjacent highlands.
  C) 3.9-3.2 billion years old, forming after most of the bombardment was over.
  D) 3.5-2.5 billion years old, similar to the formation of our own oceans.
  E) less than a billion years old, the most recent additions to the Moon.

[LVPMS]

Answer to Question 1

The conditions for feeding the active galaxy's black hole are greatly assisted by tidal interactions or even cannibalism; such collisions will be much more common in rich clusters, where the galaxies are much closer than normal.

Answer to Question 2

C

[BRWH]

Excellent

[Dnite]

Great answer, keep it coming