Black holes are among the simplest objects in the universe. They are simpler than stars, much simpler than planets, and vastly simpler than human beings.
Black holes are what is created when matter is compressed into a very small place. They are General Relativity’s most extreme prediction. They are commonly created from the violent deaths of stars many times the size of our sun, usually forming from the collapsed core of a supergiant star after it explodes.
At the heart of a black hole is a singularity. An infinitesimal point in space where the pull of gravity is infinitely strong and spacetime infinitely curved. At the singularity, space and time no longer exist as we know them. So, what would happen if we travelled into one?