As is noted in
this link, a black hole event horizon while believed to be a canonical part of the whole back hole scenario, direct evidence is hard to come by and the concept still in doubt. Researchers mentioned in the link have been able to observe a putative black hole and measure the glow of the matter falling into the black hole. Basically if there is an event horizon then the glow should be somewhat less intense than if the material is simply splashing onto a black hole's surface. Conclusion: event horizon. The take-away data graph is here:
The original article is at the arXiv.org with a link given in the linked article above.
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