This question already has an answer here:
I was hit with fridge logic, and I am curious:
Is it possible that the gravitational influence of photons inside of galaxies (And all throughout the universe) could account for dark matter?
Photons would be most concentrated close to the core and inner galaxy... And have a lessening concentration as they expanded away from galaxies due to the inverse square law..
I am struggling to understand the math involved, because I've not yet reached that level in my education.... But I'm really curious how the total photons stack up vs the measured dark matter in the universe?