A black hole, is simply the remains of a star after it dies. The original concept of a black hole was first brought up in 1795. He used Newton's law of gravity to calculate that if a object were to be compressed into a very small radius, then the escape velocity of that object would be greater to the speed of light.
When a star dies, the nuclear fusion reactions driving the star cease because all the energy required for these explosions gets burned up. At the same time, the gravity left over pulls all the material inwards towards the star. I think it does this because there is no longer any explosions to counter-act the gravity of the star. Anyway, as the star compresses, it gets hotter and eventually explodes into a supernova and all the material blasts out into space. A highly compressed, and a very big, core. The gravity is so big, that not even light itself can escape!.
The object is now called a black hole, and it now disappears from view, literally. It does this because the core's gravity is so massive it sinks through the fabric of space time! It creates a hole in space-time, which is why it is called a black hole. The core is now the central part of the black hole, which is called a singularity. The opening of this hole is called the event horizon.
Another way to think of the event horizon is as a mouth. Once something passes into this "mouth" its gone. When inside the event horizon, every "event" (things happening in space-time) stop. Nothing, not even light can get out. The radius of the event horizon is called a Schwarzschild radius.
Two types of black holes exist:.
1.Schwarzschild black hole. This type of black hole doesn't rotate.
2.Kerr black hole. This type of black hole rotates.
The Schwarzschild black hole, unlike it's name, is the simplest form of a black hole. It's core does not rotate, and it only has a singularity and an event horizon.
The Kerr black hole, which is more common in nature, rotates simply because it was formed while the star was rotating.
