You should probably be aware of the British sculptor Antony Gormley's awesome public art project, "Event Horizon." He's set up 31 casts of his own body on top of buildings around Madison Square Park in New York.
Up close, you can tell they aren't actual people. But from far away, standing on a precipice like that, they look alarming to say the least. I wonder if the NYPD has been getting calls.
They are on the horizon, sort of, but I admit I don't see what it all has to do with black holes. At any rate, it's awesome, and only further blurs the lines between street art and sanctioned public sculpture, such as they are. Many more pictures at Unurth.