Canthares was a supernova which was being used by the Daleks to test weaponry. Later, Canthares collapsed into a black hole when the Fourth and Eighth Doctors simultaneously ejected different versions of Eustace, a Fendahl skull, into it. (TV: Image of the Fendahl, AUDIO: The Dalek Trap, Island of the Fendahl)
Multiple Spacecraft became trapped in the Black hole, including the group of Daleks that had been experimenting on Canthares, Jik Gelliska and Raz Kalisto, and the Eighth Doctor (earlier in his timeline) and Lucie Miller.
All beings within the black hole fell under the control, in some respects, of the Fendahl, which was desperate to survive. It used this to influence the Eighth Doctor into reverting the formation of the black hole, knowing it was "everyone dies or no one dies", but without knowing that Fendahl was one of the beings within the black hole. (AUDIO: The Dalek Trap, Island of the Fendahl)