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

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Angular momentum and area evolution laws<br />

Area evolution law for an <strong>event</strong> horizon<br />

A(t) : area of the 2-surface St; S ɛ : volume element of St; ¯κ(t) := 1<br />

<br />

κ<br />

A(t) St<br />

S ɛ<br />

Integrating the null Raychaudhuri equation on St, one gets<br />

d2 <br />

A<br />

− ¯κdA = −<br />

dt2 dt<br />

<br />

8πT (ℓ, ℓ) + σ (ℓ) :σ (ℓ) − (θ(ℓ) ) 2<br />

2 + (¯κ − κ)θ(ℓ) S<br />

ɛ (1)<br />

St<br />

[Damour, 1979]<br />

Eric Gourgoulhon (<strong>LUTH</strong>) <strong>Black</strong> <strong>holes</strong>: <strong>trapping</strong> <strong>horizons</strong> CERN, 17 March 2010 34 / 38

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