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## Main Question or Discussion Point

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.

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.