For the first time, scientists have caught lightning in the act of unleashing a powerful burst of gamma radiation known as a terrestrial gamma-ray flash (TGF).
Researchers at the University of Osaka led the work—an intimate look at one of the most powerful and mesmerizing natural phenomena on our planet. The work also marks a step forward in the quest to understand how thunderstorms manage to pump out radiation we generally associate with the universe’s most extreme objects: black holes and neutron stars. The team’s study describing the observation was published today in Science Advances.
Using a cutting-edge multi-sensor system in Kanazawa City, Japan, the team observed a lightning discharge split between two paths—one descending from a thundercloud, the other arcing up from a ground-based transmission tower. The scientists found that a gamma flash occurred just 31 microseconds before the two discharges met in the air.
“Most TGFs have been detected by satellites, but spaceborne observations can provide limited information,” said lead author Yuuki Wada, a researcher at the University of Osaka, in an email to Gizmodo. “In this research, we performed a ground-based observation to see TGFs in detail.”
TGFs were first detected from space in the 1990s, but despite more than two decades of research, their exact origin has remained elusive. Last year, a pair of papers in Nature revealed gamma-ray “glows” and flickering flashes during tropical thunderstorms—radiation that scientists recorded by flying a retrofitted spy plane directly into storm systems. That research hinted at a wider family of radiation events lurking inside thunderclouds, with TGFs representing some of the briefest and most intense bursts.
While those plane-based observations revealed where and when TGFs occur, the Osaka team’s setup reveals the conditions in which they form. The gamma burst in this case appeared just before the two lightning leaders collided, indicating that a supercharged electric field accelerated electrons to near light speed, producing the energetic event.
“The recent Nature papers are based on airborne observations,” Wada said. “They are also very interesting, but ground-based observations can be achieved much less expensively.”
And unlike the weaker “flickering gamma-ray flashes” recently discovered in tropical skies, this TGF was tightly synchronized with a lightning strike. While the previous papers provided a sweeping overview of how many gamma-ray events occur in a given tropical thunderstorm, the recent paper scrutinized one particular event to understand how lightning produces enough energy to generate gamma rays.
“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,” said co-author Harufumi Tsuchiya, a researcher at the Japan Atomic Energy Agency, in a University of Osaka release.
Studying TGFs could help illuminate one of the most remarkable and powerful natural phenomena in our skies—so intense it was once attributed to the gods. The recent study shows that there’s more to lightning than meets the eye—its might produces radiation associated with some of the universe’s most powerful explosions.
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