Board Thread:Spoilers/@comment-87.228.248.95-20130410105423/@comment-7418318-20130410190453

But if it was, then it would run out of power sooner or later. I too think that it is more like her keys or Loke's rings and such items. It probably uses her own magic.

Either that or it has a permanent connection to the spirit realm and get's it power from there.