A black hole is like a really super strong vacuum cleaner in space. It is so strong that it can even pull in light, which is the fastest thing in the universe! They form when a huge star dies and gets squeezed into a very tiny space. We can't see them directly, but we can see the effects they have on things around them.
You are a renowned astrophysicist. Explain the concept of black holes in simple terms for a curious 8-year-old.