New research suggests that extreme objects known as “kugelblitze” — black holes formed solely from light — are impossible in our universe, challenging Einstein’s theory of general relativity . The discovery places significant constraints on cosmological models and demonstrates how quantum mechanics and general relativity can be reconciled to address complex scientific questions.
However, more exotic hypotheses exist regarding black hole formation. One such theory involves the creation of a “kugelblitz,” German for “ball lightning.” (The plural form is “kugelblitze.”)
“A kugelblitz is a hypothetical black hole that, instead of forming from the collapse of ‘ordinary matter’ (whose main constituents are protons, neutrons, and electrons), is formed from concentrating humongous amounts of electromagnetic radiation, such as light,” study co-author José Polo-Gómez
“Even though light does not have mass, it does carry energy,” Polo-Gómez said, adding that, in Einstein’s theory of general relativity, energy is responsible for creating curvatures in space-time that result in gravitational attractions. “Because of that, it is in principle possible for light to form black holes — if we concentrate enough of it in a small enough volume,” he said.
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These principles hold true under classical general relativity, which does not account for quantum phenomena. To explore the potential impact of quantum effects on kugelblitz formation, Polo-Gómez and his colleagues examined the influence of the Schwinger effect.
“When there is an incredibly intense electromagnetic energy — for example, due to huge concentrations of light — part of this energy transforms into matter in the form of electron-positron pairs,” lead study author Álvaro Álvarez-Domínguez
Einstein’s general theory of relativity states that energy, rather than mass, is responsible for the curvature of space-time that results in gravitational attractions. By this theory, black holes should be able to form from the energy of light alone. (Image credit: NASA/JPL-Caltech)
In their study Physical Review Letters
The team found that, even under the most extreme circumstances, pure light could never reach the required energy threshold to form a black hole.
“What we prove is that kugelblitze are impossible to form by concentrating light, either artificially in the laboratory or in naturally occurring astrophysical scenarios,” study co-author Luis J. Garay lasers on Earth, we would still be more than 50 orders of magnitude away from the intensity required to create a kugelblitz.”
This finding has profound theoretical implications, significantly constraining previously considered astrophysical and cosmological models that assume the existence of kugelblitze. It also dashes any hopes of experimentally studying black holes in laboratory settings by creating them through electromagnetic radiation.
Nonetheless, the study’s positive outcome shows that quantum effects can be efficiently integrated into problems involving gravity, thus providing clear answers to actual scientific questions.
“From a theoretical viewpoint, this work showcases how quantum effects can play an important role in the understanding of the formation mechanisms and appearance of astrophysical objects,” Polo-Gómez said.
Inspired by their findings, the researchers plan to continue exploring the influence of quantum effects on various gravitational phenomena, which have both practical and fundamental significance.
“Several of us are very interested in continuing the study of the gravitational properties of quantum matter, particularly in scenarios where this quantum matter violates traditional energy conditions,” said Eduardo Martín-Martínez like the Alcubierre warp drive or traversable wormholes.”
