A black hole is a place in space that is extremely dense and has a strong gravitational pull. This is because a lot of matter has been squeezed into a tiny space. This usually happens when a star is dying. Black holes can suck in entire stars and planets! Black holes can be from the size of a single atom to the size of the Sun! Black holes are still mysterious because even light can’t escape a black hole, meaning that scientists can’t see them. But, they can see the movement of stars around the black hole and study it this way. That is what black holes are!