Black holes form when enough mass gets packed so close together that its gravity gets so strong that even light cannot escape it. Mass and energy are equivalent, so theoretically it is possible to create a black hole by bringing enough energy in a different form than mass together, for instance in the form of photons. This is called a kugelblitz.

Now, is it possible to create a kugelblitz by giving a small amount of mass enough kinetic energy? As far as I know, that should work, but I'm not a trained physicist. But that leads me to my second question: a particle's speed depends on the frame of reference that is used to describe it. A particle that is at rest in one frame of reference is traveling at relativistic speed in a different frame of reference. So, why does not all mass collapse into black holes? Or is there one frame of reference that is 'special' in this regard?

  • $\begingroup$ I think this is a wonderful question, and I can tell you that the answer must be that a single particle cannot form a black hole by itself, though it can certainly have so much kinetic energy that if it impacts with anything else it forms a black hole. But how that emerges from the Einstein equations, I would really love to see worked out. $\endgroup$
    – CR Drost
    Dec 1, 2019 at 17:08
  • $\begingroup$ @CRDrost I didn't mean necessarily a single particle. What about an object travelling at relativistic speed? $\endgroup$
    – JanKanis
    Dec 1, 2019 at 17:12
  • $\begingroup$ I mean the same argument has to hold if it is all nicely uniformly moving; the only interesting detail there is that it also had to be gently accelerated because we are talking about relativity and any acceleration implies interesting forces and a failure of rigidity. $\endgroup$
    – CR Drost
    Dec 1, 2019 at 17:24
  • $\begingroup$ That question is certainly related, but that is a yes/no question regarding what happens. I want to know where the reasoning that concludes that all mass collapses into black holes goes wrong. I'll clarify the question. $\endgroup$
    – JanKanis
    Dec 1, 2019 at 20:15
  • $\begingroup$ @JanKanis The spacetime curvature created by kinetic energy is canceled out by gravitomagnetism. $\endgroup$
    – safesphere
    Dec 2, 2019 at 5:28