Does anyone know of a review article on astrophysical collapse to a black hole? There are several statements I've picked up from WP that either surprise me or that I'm not sure I understand. This Penrose diagram http://en.wikipedia.org/wiki/File:PENROSE2.PNG shows the singularity as being initially coincident with the horizon at what looks like finite r, which seems odd to me. I would have naively expected it to form at r=0, but I guess even in the Schwarzschild metric, that isn't really true; it's spacelike, not timelike, so it doesn't make sense to refer to it as having a definite position. The diagram also shows the singularity as being timelike initially before it eventually settles down and becomes spacelike. I guess this is the only way to connect the event of formation to the eventual spacelike world-line of the Schwarzschild-like singularity. This WP article http://en.wikipedia.org/wiki/Apparent_horizon says that an event horizon forms before a trapped null surface. (The statement is referenced to Hawking and Ellis, without a page number.) I guess the Penrose singularity theorem only guarantees that a spacetime that contains a trapped null surface must also contain at least one black hole singularity, but I'd been imagining that the trapped null surface would come first. I wonder where on the Penrose diagram the "apparent horizon" (boundary of the union of all trapped null surfaces) would lie.