A black hole is seen by an observer as a black disc. I understand that this is due to its strong gravitational pull that does not allow light to escape and thus it doesn’t reach the observer. I am trying to understand this situation within a Penrose diagram of Schwarzschild spacetime. The event horizon of the black hole therein is the 45° tilted line. From any point in the exterior region, the past light cone consists of events that are in the exterior region or in the white hole. Thus, I do not understand how this black disc arises. As the events seen by observer consists only of those on the past lightcone, there should be some kind of "obstacle" within the Penrose diagram that blocks the light from reaching the observer, creating the prominent black disc. But the black hole (i.e., the event horizon) lies only within the future (!) light cone of any event in the exterior region. How can the black hole be seen as a black disc, if it lies in the future?