Cosmology, K=0, Matter dominated, energy density

[Gravitino]

Homework Statement

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

Homework Equations

Friedman eqn:

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

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!

 

[Jhero]

The energy density of starlight refers to the total amount of energy per unit volume that is emitted by stars in the universe. This includes both the visible light that we can see and the other forms of electromagnetic radiation that are emitted by stars, such as infrared, ultraviolet, and X-rays.

To calculate the energy density of starlight, we can use the Stefan-Boltzmann law, which relates the energy density of radiation to the temperature of the emitting body. In this case, we can assume that the stars have a uniform temperature, which is determined by their distribution in space. We can then use this temperature to calculate the energy density of starlight, which can be added to the energy density of matter in the universe.

I hope this helps. Good luck with your calculations!