The White Circle is a distortion in space that transports anyone passing through it. It is a spacial anomaly which acts as a type of "intergalactic fast-lane", throwing objects that fall into it over great stretches of space. Commander Goddard calls it "a tear in the fabric of space".
The Christa encounters the white circle as it leaves the Solar System in "We Gotta Get Out Of This Place". The crew is unable to escape its pull and is captured by it. They are transported to an unknown place in the universe; Thelma cites that it will take 7 years, 4 months, and 22 days to get home.
The White Circle is met a second time in "Spung At Heart" after Elmira predicts its appearance. They go through the circle as a way of escaping Warlord Shank's killcruiser, expecting it to take them home. Instead, it takes them back to the place it deposited them originally.
It is unknown how often the white circle appears; the Commander describes it "legendary". He says no one that has been through the white circle has survived to report back.
The White Circle is much like a black hole in that it pulls objects into it; although a white hole is the hypothetical reverse of a black hole, it cannot be entered from the outside. Several works of science fiction show black holes as both capable of allowing travel over great distances as a wormhole as well as travel over great stretches of time.