A black hole is the remnant of a massive collapsed star.
Birth of a Black Hole
A black hole forms when a massive star implodes. All of the star's outer layers explode into a supernova, while the core is so heavy that it shrinks down to the fraction of an atom. Then, the star shoots out a gamma ray burst and turns into a black hole.
Black holes are classified into 3 groups: stellar mass black holes, supermassive black holes, and hypermassive black holes.
Stellar mass black holes are the smallest black holes, but they have the strongest gravitational pull of any type of black holes. They are usually the size of an asteroid but they can be up to 2-4 solar masses.
Supermassive black holes range from the size of Arcturus all the way to the largest stars. Their mass ranges from 4 million to 4 billion solar masses.
Hypermassive black holes are the largest black holes in the universe. They range from 4 billion to 200 billion solar masses.
Black holes have the strongest gravitational pull of any object in the universe. They are split into 4 sections: The accretion disk, the event horizon, the Cauchy horizon, and the singularity.
The accretion disk is the matter that orbits a black hole, since matter that is a little too far away to get swallowed by the monstrous object gets trapped in its orbit.
The event horizon is the black part of the black hole, and is the point of no return. Not even light can escape.
The Cauchy horizon is the inner part of the event horizon, where matter that gets swallowed by the black hole gets spaghettified by the black hole. All matter will become one atom wide was it enters this part of the black hole.
The singularity is the part where anything that gets swallowed by the black hole ends up. The singularity holds no space, but is infinitely dense.