Recently, I read a quora post in which the OP asked the following question: Can a black hole be formed from accelerating a body and increasing its relativistic mass to the level of a Schwarzschild black hole? This question had me confused because of an apparent conflict of principles:
On the one hand, a well received answer to the quora post suggests that formation of black holes are only dependent upon the invariant rest mass, instead of the relativistic mass. Therefore, acceleration of any body to arbitrary speed would not cause a black hole to form. (See: https://www.quora.com/Is-it-possible-to-accelerate-matter-so-much-that-it-becomes-a-black-hole-in-one-frame-of-reference-and-not-in-another)
On the other hand, a quick search on wikipedia indicates that kugelblitz (black hole formed from concentration of energy, possibly with zero rest mass) is theoretically possible.
So my questions are:
Are there theoretical models for how a kugelblitz could possibly form? (The wikipedia page mentioned Wheeler's geons. But I do not have access to his paper and cannot tell if geon solutions are actually black hole solutions in any sense)
If the answer to question 1 is yes, energy can indeed create black holes. So, from some reference frame A moving rapidly away from the earth (or really anything for that matter), will the earth have enough energy density to become a black hole in A?
Personally I believe that both answers should be no. But I'd love to hear from experts who know a lot more to judge.