Sentilli was a black hole located in the Andromeda Galaxy.
History[]
At some point in the black hole's history, the Cult of Shining Darkness placed a colossal space station known as "the Torch" inside the black hole. The station had a very powerful shielding and so remained intact.
Much later, a faction of the Cult arrived in the Sentilli System with a device that would open the black hole and allow the station out. They intended to use the station to control all the robotic life forms in the Andromeda Galaxy. They would then use the robots as an army to enforce their view of the supremacy of organic beings over non-organic life. However, the Tenth Doctor and Donna Noble, along with the crew of the Sword of Justice, defeated the Cult and sent the station back into the black hole with its shields down, which would destroy it. (PROSE: Shining Darkness)