Okay, so the question that I am curious about this for, specifically says "A supernova remnant has an angular diameter θ = 4.3 arcminutes and a flux at 100 MHz of F100 = 1.6×10−22 Jm−2s−1Hz−1. Assume that the emission is thermal."
Does that help at all? I figured that to calculate the value of...
Is it anything to do with the equation being independent of mass etc.. of the star? or to do with the Pauli exclusion principle? Any help will be much appreciated.
The only solution (for part a) I can think of is if we use the radiative transfer equation without S... i.e. $$\frac{I}{\tau}= I_0 e^{-\tau}$$ and then take the natural log of each side to get $$\tau= -\ln(\frac{I}{I_0})$$ but I don't know if I can just get rid of S like that?