Matter density parameter
= Matter density parameter
{title2=$\Omega_m=\rho_m/\rho_{\rm crit}$}
The <matter density parameter> is the ratio of total nonrelativistic matter density, including baryonic and <dark matter>, to the <critical density> $\rho_{\rm crit}=3H^2/(8\pi G)$ at the same epoch. A present-epoch value uses $H_0$ and $\rho_{m,0}$. It is not the total <cosmological density parameter> when radiation or vacuum <energy> also contributes.