jaLissajous

jaLissajous t1_j24vr8k wrote

In the cosmological context the current contribution of photons to the energy density of free space is negligible.

However there are entirely theoretical phenomena that occur under extreme radiation-dominated energy densities. Most notable is the Kugelblitz: a black hole formed by concentrating light (or heat) sufficiently dense as to curve spacetime and create an event horizon. This entirely theoretical black hole is one of a class of phenomena proposed by Wheeler in 1955 called "Geons" in his paper of the same title.

A model of these (again theoretical) geons has been extended to a candidate for dark matter called Graviballs. Which is a neat idea, but has no supporting observational evidence that I'm aware of.

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