Eye of Harmony

The Eye of Harmony was a black hole used as a power source for TARDISes, kept on Gallifrey, however all TARDISes had a remote link to it inside. (DW: The Three Doctors, Doctor Who: The TV Movie)

History
While experimenting with time travel, the Time Lord Omega created the very first black hole, but fell into it, into an anti-matter universe created by his willpower. The black hole was later captured and placed on Gallifrey as a power source. (DW: The Three Doctors)