Stasis halo

In the early history of the Time Lord civilisation, stasis haloes protected the ships of a Gallifreyan fleet from "the maelstrom" of a growing black hole, which would have given them the power of time travel.

Fenris the Hellbringer, agent saboteur of the Order of the Black Sun, infiltrated the flagship Aeon and with a wave scrambler he operated on the stasis field generator, switching off the protective haloes. The whole fleet was to be sucked into the black hole; in particular Omega's ship broke up because of the gravitational pressure. The secret intervention of Rassilon switched back on the haloes and saved the rest of the fleet. (COMIC: Star Death)