= Oppenheimer-Snyder model
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{wiki=Oppenheimer–Snyder_model}
= Oppenheimer-Snyder collapse
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The <Oppenheimer-Snyder model> describes a homogeneous ball of <pressureless matter> collapsing from rest, with a closed <FLRW metric> inside and a <Schwarzschild metric> outside. In geometric units its interior is $ds^2=-d\tau^2+a^2(d\chi^2+\sin^2\chi\,d\Omega^2)$, with $a=a_{\max}(1+\cos\eta)/2$ and $\tau=a_{\max}(\eta+\sin\eta)/2$. The boundary is a fixed comoving angle. <Density> conservation gives $\rho a^3$ constant, and the <Friedmann equation> at the initial turning point gives $8\pi\rho_0a_{\max}^2/3=1$.
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