Depends on whom you ask. A physicist will have a different view to a chemist. As a chemist, sometimes my office seems like a black hole when I am looking for something.
Perhaps more a question for the physicists! As I understand it, a black hole isn’t so much a substance as a chemistry would understand it, but a region of spacetime where gravity is so intense not event light can escape.
The truth is that we don’t know for certain what the inside of a black hole is like! Black holes are centres of such extreme gravitational attraction that ANYTHING—matter and even light—that gets too close “falls” in. What happens to matter in such an extreme environment though is very much an open question and an intense area of research. However, that research is mainly the realm of physicists not chemists!
On the outside, the stuff going into the black hole is made up of normal atoms. However, as we go into the black hole, the gravity is so strong it can force the electrons, protons and neutrons together to have something that I think is called degenerate matter. We can find this type of matter on neutron stars. However, inside the black hole, we can’t really think of matter as the black hole has no size. It is zero dimensional… a point.
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