Thought to occur naturally by human astrophysicists, the Doctor
stated that the Time Lords invented black holes. (DW: The Satan
Pit) Probably more so meaning that they pioneered creating black
holes artificially, not necessarily that they never occur
naturally. There are a lot of them, and the Time Lords would
have to be very busy indeed to have created them all. Omega and
Rassilon destroyed the star Qqaba (DWM: Star Death) as an energy
source powerful enough to enable time travel. Omega, thought
dead, survived his journey through this black hole, although he
was trapped within it. He was also able to shape matter within
it to his will. (DW: The Three Doctors, Arc of Infinity)
Rassilon brought back either a black hole or its singularity, no
one knows which, to become the Eye of Harmony back on Gallifrey.
(DW: The Deadly Assassin) The Doctor's TARDIS had the power both
to resist the pull of the black hole and also to tug the Walker
Expedition's rocket out of the gravitational field of the black
hole K37 Gem 5.