# Cosmology, K=0, Matter dominated, energy density

1. Oct 26, 2008

### Gravitino

1. The problem statement, all variables and given/known data

For K=0 of matter dominated universe, i.e at z>>1, find the enery density of starlight if f portion of matter condensed in solar type stars and the stars are uniformly distributed in space.

2. Relevant equations

Friedman eqn:

$$\rho_m = \frac{3H^2}{8 \pi G}$$

3. The attempt at a solution

This is homework, so i do not want someone simply to solve it for me. My concern is what do they mean by the energy density of starlight? And is it not the same as proper energy density that i brought above in Friedmann equation? (The notion for this energy density was U*). I need some hints. Thanks!