Q. A ‘black hole’ is a body in space which does not allow any radiation to come out. This property is due to which of the following features?
Answer: very high density
Notes: A black hole is a region of spacetime where gravity is so strong that nothing, not even light or other electromagnetic radiation, can escape from it. This extreme gravitational pull results from a massive object being compressed into a very small volume, creating what is known as a singularity—a point where density and gravitational forces become infinite, posing significant challenges for modern physics. Black holes are theorized to emit Hawking radiation, but for stellar-mass black holes, this radiation corresponds to temperatures of only billionths of a kelvin, making it virtually impossible to detect with current technology. The density of a black hole depends on its mass and how one defines its size. While the singularity at its center is thought to have infinite density, the average density of a black hole (calculated using its mass and the volume within its event horizon) decreases as its mass increases. For comparison, ordinary materials on Earth range in density from lightweight aerogels (as low as 0.001 g/cm³) to osmium, the densest naturally occurring element, with a density of 22.61 g/cm³.