What are black holes

Black holes are areas in space where the gravitational pull is so strong, not even light can escape it. That's why they are invisible. The reason black holes have so strong gravity is because there's so much mass crammed inside a small area. Some black holes pack 3 times the sun's mass into a city-sized area.

Different types of black holes

There are three different types of black holes. What determines the type of black hole is its size. There are smaller ones, called miniature black holes. There are the average sized ones called stellar black holes, and then there's the supermassive black holes, which are the biggest.