Things that are pulled into the enormous gravity of a black hole become part of it.
Unlike a hole in your sock, a black hole is not an opening; it’s the term for a dead star with a very strong gravitational pull. When a big star—much more massive than our Sun—uses up all its fuel after a few million years, it collapses, which means that it squeezes its core tightly together and crushes down to almost nothing. In the small region around this super-dense, super-small object, nothing can escape. Things pulled in by its gravity become part of the compressed mass.
Art by: Victor Davila