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Black holes: from event horizons to trapping horizons - LUTH ...

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Local approaches <strong>to</strong> black <strong>holes</strong><br />

What is a trapped surface ?<br />

2/ The definition<br />

S : closed (i.e. compact without boundary) spacelike 2-dimensional surface<br />

embedded in spacetime (M , g)<br />

Being spacelike, S lies outside the light<br />

cone<br />

∃ two future-directed null directions<br />

orthogonal <strong>to</strong> S:<br />

ℓ = outgoing, expansion θ (ℓ)<br />

k = ingoing, expansion θ (k)<br />

In flat space, θ (k) < 0 and θ (ℓ) > 0<br />

Eric Gourgoulhon (<strong>LUTH</strong>) <strong>Black</strong> <strong>holes</strong>: <strong>trapping</strong> <strong>horizons</strong> CERN, 17 March 2010 11 / 38

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