Possible spacelike foliations of a geometry of a black hole collapse. The outer cylinder represents the AdS boundary, the bottom (orange) surface a collapsing star, the (red) vertical line the curvature singularity, and the inner (purple) cylinder the event horizon. Two distinct sets of foliations are sketched. On (a), the corresponding apparent horizon has settled down at late time (indicated in blue). On (b), the spacelike surface (green) at admits no apparent horizon at all.
