Question

What can be detected within the event horizon a black hole?

Answer 1

Nothing can be detected within the event horizon of a black hole.

Explanation:

By definition, the event horizon of a black hole is a boundary from which nothing can escape, not even light. This means that we can't see beyond the event horizon without passing through it and never be able to return.

Black holes defy our understanding of physics. It may be possible that future physics may change this.