Equestria could have a different system of its own. After all, you can walk right into Tartarus without much trouble. Then again, if the Pale Pony could swallow an entire Equestria, then perhaps things are different there. Those who die or disappear from this Equestria get taken to the Pale Pony, don't they?

(She rubs her chin in thought.)

Perhaps that in itself is a matter worth investigating...