K37 Gem 5

K37-Gem-5 was the designation of a black hole five hundred years from Earth. In the 44th century, a Human empire sent two expeditions, the Galis Expedition and later the Walker Expedition to the vicinity of the black hole in order to find what kept a planet in stable orbit around the black hole. While the Doctor, Rose and the crew of the Walker Expedition watched, the black hole the Scarlet System fell into the gravity sink of the black hole.

When Rose said that she thought that some black holes might lead to other universes, the Doctor said that this one did not. (DW: The Impossible Planet, The Satan Pit) In actuality, the black hole and the planet served as a prison for the Beast. (DW: The Satan Pit)