Board Thread:Roleplaying/@comment-26841958-20150805134012/@comment-6881629-20150805160317

The Mace of Molag Bal has the soul trap enchantment and that works on any souls black or white, Azura's Star can only contain white souls where as the Black Star only black (but a bug means it can actually contain both).

So if you want to trap the souls of people you have to pick the Black Star otherwise it's up to you.