Spatial projection of extremal surfaces in Vaidya-AdS (collapsing black hole) geometry, calculated at various times in the black hole formation process. The outer (black) circles correspond to the AdS boundary at time given by the indicated; the inner (red) circles correspond to the event horizon cross-section at corresponding time. The remaining curves correspond to the extremal surfaces anchored on the boundary, colour-coded by the size of the boundary region they encompass. At early times before the black hole forms, these extremal surfaces coincide with minimal surfaces in pure AdS. We can see that as the black hole grows, these surfaces are “repelled” to remain outside the horizon.
