Can photons form black holes the same way as other matter? If there happens to be enough of them concentrated in an area of space so that enough energy exists within a radius to form an event horizon, will an actual inescapable black hole then come into existence?
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3$\begingroup$ Yes : en.wikipedia.org/wiki/…. $\endgroup$– jensen paullCommented May 15, 2023 at 16:04
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1$\begingroup$ I'm astounded that so many responses seem ignorant of the literature, including MTW's Gravitation (which explicitly discusses the stress-energy tensor of the electromagnetic field) and the references linked to from the Wikipedia article including Wheeler's 1955 Geon paper. Of course a Kugelblitz is possible (if unlikely) and it has been known since Tolman's 1931 paper that counter-propagating beams of light attract each other (and everything else, i.e. they bend spacetime). $\endgroup$– Eric SmithCommented May 16, 2023 at 20:46
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$\begingroup$ @EricSmith "I'm astounded that so many responses seem ignorant of the literature" - Exactly! How dare these heretics to doubt The Book! Especially those claiming the Earth is not flat - they must be burned alive and their comments deleted by the moderators. $\endgroup$– safesphereCommented May 19, 2023 at 4:04
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$\begingroup$ @EricSmith Perhaps you may find it interesting that photons in flight don't bend spacetime: iopscience.iop.org/article/10.1088/1367-2630/18/2/023009 - This invalidates any solution treating electromagnetism in gravity as a classical field. $\endgroup$– safesphereCommented May 19, 2023 at 4:08
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Einstein's field equations couple to the stress-energy tensor, with the $T_{00}$ component dominating. Since $E=mc^2$, mass is usually the dominate form of energy density; however, any energy density will work.
If it's light: the resulting blackhole is called a Kugelblitz.
Nevertheless, from the outside, it still has no hair and is described by mass, spin, and charge (so far, classically).
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$\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Physics Meta, or in Physics Chat. Comments continuing discussion may be removed. $\endgroup$– rob ♦Commented May 17, 2023 at 3:57