I Dark Matter as a condensation of photons in a space

[ahmashojaeddin]

TL;DR Summary

could we think of DARK MATTER as condencation of photons in a space (eg. galactic space) that not yet escaped from that huge wide space due to limitaion of light speed?

if we assume each photon of light as a very very light piece of matter (by famous E = mc^2 and then: m = E / c^2) and sum up all photons that have been made from the creation time of a galaxy (also considering limitation of speed of light) and also photons that accidentally passing throw that galaxy (eg. coming from other galaxies), could we result that, relativistic mass of these photons can act as matter that can curve space-time and doing like DARK MATTER as they don't emmit photons and do not absorb or reflect them?

 

[Bandersnatch]

1) You can't use $E=mc^2$ for photons, since m stands for rest mass and photons have none. The full equation is $E^2=(mc^2)^2+(pc)^2$, which for zero rest mass reduces to $E=pc$, where p is momentum.
2) The energy of photons does contribute to gravity, similar to mass. But it's negligible at current epoch in the history of the universe, due to it diluting with the expansion of space faster than any other kind of energy. The only time when there was enough energy in photons in the universe to count for anything was back when the universe was still opaque to light. All the observation suggesting dark matter come from later epochs, and require behaviour different than that of light (such as forming localised overdensities).
3) Photons don't emit photons, but they are photons. Which means they are observable. A shining light bulb is not dark.