Hi, Alexis. The black holes are little start very, very dense, with a huge gravitational field that is so strong that pulls even electromagnetic waves, in other words, the light. That's why we call them black holes, because when observed, you kind of see a lack of emission there. Depending on the initial mass of a star, it will have a different fate in the end of its life. For stars similar to our Sun, at the end of their lives, they will become a "white dwarf". For stars with bigger masses (2 to 3 times the solar mass), at the end of their lives, they become "black holes".