Empty.

Description
Empty. (AKA Frog's Void) Is a very small "universe" (though it's only a couple hundred light years in diameter). Anything that enters the Empty begins quickly fading away, one atom every planck-time, which doesn't sound very fast, but (to my understanding of the calculations) this means you will be deleted in under half a second. It is physically impossible for anything to exist here for more than 10 seconds. Empty is completely invisible, so it's impossible to know it's exact location without throwing something in there.

Discovery
Empty was discovered when a fleet of explorer ships flew into it when coming back from a classified mission. Some ships suddenly disappeared, which pointed the Empty out to the others who noticed.