A black hole made of pure light is impossible, thanks to quantum physics

In recent years, science fiction writers have seized on the mystique of the kugelblitz and chased after it. Fans of the Netflix show Umbrella Academy may be familiar with the term, which is German for ball lightning. In season 3, a kugelblitz wipes out large swaths of existence.

In general relativity, gravity results from the curvature of matter in spacetime. If enough mass is packed into a region, spacetime can bend so dramatically that it forms a region within which it is impossible for a black hole to escape. But in general relativity, energy and mass are equivalent. This means that energy can bend space-time just as matter can, suggesting the wild idea that a black hole can form without matter at all.

This concept is a very interesting thought, says theoretical physicist Juan Garca-Bellido of the Universidad Autnoma de Madrid, who was not involved in the new study, especially if we want to produce something like this in the laboratory. Scientists have previously looked into whether futuristic lasers could one day form a black hole in a lab, and have even proposed using a kugelblitz to power a spacecraft.

Alas, the calculations suggest that any attempt at a kugelblitz would result in failure, Martn-Martnez says. You won’t even come close. You won’t even get something that starts to appeal to you like Earth.

This is due to a quantum effect that occurs when electromagnetic energy is highly concentrated. According to the well-proven theory of quantum electrodynamics, when light reaches those extremes, pairs of particles and antiparticles begin to form. Those electron particles and their positively charged antimatter partners, the positrons, will escape the region, taking energy with them. This prevents the energy from reaching the levels needed to form a black hole.

Forming a kugelblitz in a laboratory would require light intensities greater than 10⁵⁰ times more than the latest laser pulses, the team calculated. (That’s an extremely large factor of 1 with 50 zeros behind it.) And in nature, the brightest quasars—the brilliant centers of active galaxies—are also very dim.

The kibosh on kugelblitzes applies to a wide range of scales. It excludes kugelblitzes with a radius as small as one hundredth of a quintillionth of a nanometer to 100 millionths of a meter. Even outside that range, Martn-Martnez says, a kugelblitz would still be highly unlikely.

Garca-Bellido, however, points to a potential loophole: It’s much more likely that such things happened in the early universe.

Just after the Big Bang, the universe is thought to have expanded extremely rapidly, a process known as inflation. This inflation may have introduced fluctuations in the curvature of spacetime that could cause light to collapse into what is known as a primordial black hole (SN: 8/7/16). So while light won’t form black holes under its own gravity, that preexisting curvature, Garca-Bellido says, could have allowed for something akin to a kugelblitz.