What is thing called black hole?
In short, black holes are points in space which have zero volume and infinite density. Its a vacuum in a vacuum. Imagine the mass of a million solar systems crammed into the space of an atom. That’s the reason the gravitational pull is so strong. Gravity between two bodies is proportional to the product of the two masses and inversely so to the square of the distance between them. Mass is huge, and its radius is virtually zero. Imagine the force! The ‘supermassive’ blackhole at the centre of the Milky Way may not be larger than Mars, yet the damn thing can hold the entire galaxy together. The gravitational pull is so strong, even light, with a velocity of 300,000,000 m/s can’t escape. That’s the reason why black holes are invisible.
