If something like a spaceship or a moon was falling towards a black hole and happened to cross the event horizon what would that look like to outside observers? On one hand, photons can not escape at that point, so the object should no longer be visible. On the other hand, the object's time will seem to slow down from the point of view of outside observers.
So, will the people watching it see the object pop out of existence at some point, or will it look it just hangs there forever or will some other effects occur? And if it does disappear from view how long will it take (or what would be the formula, since actual time will probably depend on black hole size and distance from the observers)?