While light and black holes may seem like opposites, general relativity reveals they share surprising similarities. Einstein's equations show that, much like a collapsing star, concentrated light can form a black hole.
In January 1955, renowned American physicist John Archibald Wheeler, a leading expert in general relativity and black holes, published "Geons," exploring how electromagnetic waves interact with gravity (1). Wheeler examined how an electromagnetic wave could be trapped in a spacetime region by the gravitational pull of its own energy.
Using general relativity's gravitational field equations, Wheeler demonstrated that confining a massive amount of photons in a tiny spacetime region creates extreme energy density, leading to an event horizon and a black hole (1). He coined the term "kugelblitz," meaning "ball lightning" in German.
General relativity is fundamentally a theory of energy, not just mass. Gravity arises from energy's curvature of spacetime, with E=mc² linking energy and mass. Thus, massless photons feel gravity like massive objects and produce gravitational fields.
A kugelblitz behaves identically to a "classic" black hole, differing only in formation. Unlike stellar black holes (from star collapse) or primordial ones (from early universe density fluctuations), a kugelblitz forms from photon concentration so intense it traps the light within an event horizon (2).
Once formed, it's described by the Schwarzschild metric, same as other black holes. General relativity treats all event horizons equivalently, regardless of origin.
Wheeler's concept has been expanded by physicists, including feasibility of artificial kugelblitz creation. However, forming an Earth-sized one requires the light from all stars within a 350-light-year radius for ten years (2)—an astronomical feat.
