Crucible of Souls

The Crucible of Souls, located on an asteroid, was an invention of the Doom Coalition. It was created in order to convert the life energy of the people at the end of the universe into regeneration energy to make the Time Lords immortal.

The Nine intended to use it to give himself immortality, and become "the Numberless" or "the Eternity". (AUDIO: The Crucible of Souls)