plural of rock hole

plural of supermassive black hole

plural of Schwarzschild black hole

plural of Kerr black hole

plural of BTZ black hole

plural of optical black hole

plural of primordial black hole

plural of regular black hole

A small hole in a steam boiler for the insertion of the hand in cleaning, etc.

(astrophysics) A theoretically possible, but physically highly unlikely, singularity from which matter and energy are able to escape but unable to enter; the antithesis of a black hole.