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When lightning strikes: Gamma-ray burst unleashed by lightning collision

Lightning is a phenomenon that has fascinated humanity since time immemorial, providing a stark example of the power and unpredictability of the natural world. Although the study of lightning can be challenging, scientists have, in recent years, made great strides in developing our understanding of this extreme spectacle.

A study published in Science Advances, led by researchers from The University of Osaka, describes a world-first observation of an intense burst of radiation, known as a terrestrial gamma-ray flash (TGF), synchronized with a lightning discharge.

"The ability to study extreme processes such as TGFs originating in lightning allows us to better understand the high-energy processes occurring in Earth's atmosphere," explains Yuuki Wada, lead author of the study.

It had been hypothesized that TGFs arise from lightning discharges as a result of the acceleration of electrons to very high speeds. However, the transient nature of this phenomenon, which lasts for only tens of microseconds, made it difficult to confirm this hypothesis.

In this study, a state-of-the-art multi-sensor setup was used to observe TGFs emerging from lightning storms in Kanazawa City, Ishikawa Prefecture, including optical, radio-frequency, and high-energy radiation.

Two discharge paths were observed, one descending from the thundercloud to the ground-based transmission tower and one ascending in the opposite direction. The researchers found that a TGF occurred just before the two discharge paths met, creating a highly concentrated electric field that accelerated electrons in the air to near light speed.

The first TGF photon was observed 31 microseconds before the collision of the discharge paths, and the full burst lasted for 20 microseconds after they met to form the lightning strike. A discharge of −56 kA occurred as a result of the collision of lightning leaders.

This observation contributes critical data to the longstanding mystery of how lightning generates enough energy to produce gamma rays—phenomena typically associated with outer space events like supernovae or black hole jets. The study also supports emerging theories about lightning leader dynamics and the potential role of thermal runaway or relativistic feedback in these extreme bursts.

"The multi-sensor observations performed here are a world-first; although some mysteries remain, this technique has brought us closer to understanding the mechanism of these fascinating radiation bursts," says Harufumi Tsuchiya, senior author.

The research offers not only a rare glimpse into the inner workings of lightning, but also valuable data that could be used to improve the safety and resilience of structures vulnerable to high-energy atmospheric phenomena.