In theoretical physic, a kugelblitz (German: “ball lightning”, not to be confused with ball lightning) is a concentration of light so intense that it forms an event horizon and becomes self-trapped: according to general relativity, if enough radiation is aimed into a region, the concentration of energy can warp spacetime enough for the region to become a black hole (although this would be a black hole whose original mass-energy had been in the form of radiant energy rather than matter). In simpler terms, a kugelblitz is a black hole formed from energy as opposed to mass. According to Einstein’s general theory of relativity, once an event horizon has formed, the type of mass-energy that created it no longer matters.