Here we go: A black hole is like a cosmic jail of condemned prisoners. You can check in but you can’t check out. Suppose you throw a ball up into the air. It falls back down on the ground. Now throw it up at a speed greater than 40,000 kilometers per hour, which is Earth’s escape velocity, and it will not return. Escape velocity is the key to understanding black holes. If you can squeeze Earth’s mass into a smaller size by using a giant vice, its escape velocity would rise. After the circumference is reduced to less than 5.6 centimeters, its escape velocity would become greater than the velocity of light, which is about 300,000 kilometers per second. Since nothing can go faster than light, nothing could escape from our compressed Earth – it would become a black hole. Thereafter, gravity would cause Earth to continue to collapse until it is reduced to what is called singularity – a point of infinite density. The space around it would be curved like a rubber sheet with a heavy steel ball in the middle. Enclosing the singularity would be spherical event horizon. Anything that happens inside that sphere would remain hidden from the observers outside the sphere, because any light emitted inside is unable to escape. Without emission of light, Earth would be as black as, yes, a black hole.
- Why is it not possible to see a black hole?
- What do black holes in the universe look like?
- When our Sun becomes a black hole, would it gobble up the Earth?
- Where had the Big Bang happened? Where is the center of the universe?
- When was the existence of black holes predicted for the first time? And by whom?