K37 Gem 5

K37 Gem 5 was the designation of a black hole which served, along with the planet that orbited it, as a prison for the Beast.

Anomalies
A lifeless rocky planet (Krop Tor) that maintained a (mostly) stable stationary orbit in violation of the laws of physics. First the Galis Expedition and later the Walker Expedition traveled to the planet, the latter from Earth via a gravity funnel emanated by the planet. The Walker Expedition hoped to secure a new power source for their empire, in order to save it, a power source great enough to stay the planet from falling into a black hole. The Doctor and Rose Tyler found the Walker Expedition in 43K2.1. (TS: Tardisode 8, DW: The Impossible Planet)


 * The gravity funnel itself, generated by the planet, presented a mystery. To be able to generate the amount of gravity the planet generated, it would have to generate 6 to the power of 6 metres every 6 seconds.


 * The location of the black hole is not known, other than the Doctor's description of the black hole as out in the depths of the universe. He also stated that if you travelled 500 years in a certain direction, you would reach Earth. Unless the Doctor's comment was suggesting that the speed would be slower than that of the Walker Expedition's spacecraft. This seems to contradict the fact that the crew expected to return to Earth in less than one human lifetime, without cryogenics or other means of surviving centuries-long journeys.

Effect on history
Local legends the ones that had attracted the Galis Expedition originally, had accrued about the black hole and the planet. One, myth, held by the Valtino, described the black hole as a demon. Walker Expedition team member Ida Scott said the mere sight of the black hole tended to drive onlookers insane.

As the Doctor, Rose and the crew of the Walker Expedition watched, the Scarlet System, home system of the Pallushi fell into K37 Gem 5's gravity field. (DW: The Impossible Planet)

In actuality, the black hole and the planet served as a means for the Disciples of the Light to imprison the Beast. (DW: The Satan Pit)

Behind the Scenes
The black hole special effect was re-used in Invasion of the Bane, with the addition of some tumbling meteorites or asteroids.