The property of a black hole that prevents any radiation from escaping is due to its very high density.

A black hole is formed when a massive star collapses under its own gravitational force, resulting in an extremely dense and compact object. The gravitational pull of a black hole is so strong that nothing, including light, can escape its gravitational field once it passes a boundary called the event horizon.

The high density of a black hole is a result of its mass being compressed into a very small volume. This immense concentration of mass creates a gravitational field so intense that even light cannot escape, giving rise to the concept of a black hole. The size of a black hole, in terms of its event horizon or Schwarzschild radius, is determined by its mass.

Therefore, the property of not allowing any radiation to come out is primarily due to the extremely high density of a black hole rather than its size or low density.