No-one can or ever will observe an event horizon. It's a theoretical mathematical construct with no physical reality. It's also in a region permanently hidden by view. It's also (in my submission m'lord) not formed yet.What we see is the radiation emitted by matter that has come under the influence of a gravitational field so strong and so localised that we believe it could not be explained by anything other than a BH.It's a proof by exclusion ie not a proof by construction. Mathematicians love those, but in the real world there's always another possibility.