Kugelblitz

A kugelblitz is a black hole made from light. In general relativity, all energy bends space, not only mass, so in principle enough light squeezed into a small enough space would collapse under its own gravity and close behind an event horizon. The name is German for “ball lightning”. Once formed, a kugelblitz would be indistinguishable from any other black hole, because a black hole keeps no trace of what it was made from.

Wheeler’s geons

The idea goes back to John Wheeler, who in 1955 published a paper called “Geons”, short for gravitational electromagnetic entities: bundles of light and gravity holding themselves together. A kugelblitz is the extreme case, where the light is concentrated so much that it becomes a black hole. Whether geons could ever be stable is still an open question, and most physicists think they probably cannot.

Why light may not be enough

In 2024 Álvarez-Domínguez, Garay, Martín-Martínez and Polo-Gómez published a short paper in Physical Review Letters with a blunt title: “No Black Holes from Light”. The problem is quantum physics. When the electric field of light passes about 1.3 × 10¹⁸ volts per metre, empty space starts turning light into pairs of electrons and positrons. This is the Schwinger effect. The pairs fly out of the region and carry the energy away faster than it can pile up.

They found that this rules out a kugelblitz with a radius anywhere from 10⁻²⁹ metres to 10⁸ metres, from far smaller than any particle to about a quarter of the distance to the Moon. To make one a metre across, a laser would need to deliver about 10⁸³ watts per square metre. Today’s most powerful lasers reach 10²⁷. Science News put the gap as more than 10⁵⁰ times, “a 1 with 50 zeroes after it”. Even the brightest quasars, about 10⁴¹ watts, fall far short. “No known source in the current universe would be able to produce it,” said Martín-Martínez.

Not settled

The study assumes the light flows in steadily, and a sudden, rapidly changing burst might behave differently. In December 2025 Don Page replied in the same journal. He agreed that a kugelblitz is highly implausible in our universe, but argued that in idealised collisions of light pulses, black holes could form purely from photons, at any size down to near the Planck length, about 10⁻³⁵ metres. Juan García-Bellido, who was not part of either study, has suggested that the early universe would have been a far more likely place for such things than anywhere today.