Tiny black holes, born right after the birth of the universe, are supposed to evaporate — shedding mass as invisible particles. This was predicted by Stephen Hawking, and this 'Hawking evaporation' contributed to the expansion of the young cosmos.
However, if particles exist beyond the familiar physics, a cloud can condense around a spinning hole. It acts like a thief: siphons off rotational energy and immediately blows it on space-time ripples — an effect discovered by Roger Penrose and called superradiance.
Simulations showed: the cloud almost completely intercepts the spin, leaving mere crumbs for Hawking evaporation. Gravitational waves also affect the universe's expansion rate, but only when the cloud releases them in sync with the evaporation. Otherwise, the ripples smooth out and lose strength.
Primordial black holes could be tiny — the size of an atom, but as heavy as a large mountain.
In 'Interstellar,' the black hole Gargantua could have been cloaked in an invisible thief cloud, stealing its spin.