Japanese scientists who set up custom-made sensor banks trying to understand the association between lightning strikes and high-energy gamma-ray bursts ended up witnessing a “shocking” event: the acceleration of electrons to near light speed.
Although previous studies have noted the presence of high-energy gamma-ray bursts during lightning storms known as terrestrial gamma-ray flashes (TGFs), these unexpected occurrences are typically associated with extremely high-energy space events like supernovae or black holes. Now, the University of Osaka scientists say their study is the first to explain how the acceleration of electrons causes TGFs.
“The multi-sensor observations performed here are a world-first,” explained Harufumi Tsuchiya, the study’s senior author. “Although some mysteries remain, this technique has brought us closer to understanding the mechanism of these fascinating radiation bursts.”
Gamma Ray Bursts Too Powerful for Lighting?
In science fiction, lighting is integral to everything from superhero transformations to a time-traveling, lightning-powered DeLorean. In the real world, these natural events unleash significant enough energy to start fires, knock out power transformers, or even kill. However, scientists have difficulty explaining how comparatively low-power lighting strikes could discharge the massive bursts of gamma rays typically associated with powerful astronomical phenomena.
“It had been hypothesized that TGFs arise from lightning discharges as a result of the acceleration of electrons to very high speeds,” the researchers explain in a statement. “However, the transient nature of this phenomenon, which lasts for only tens of microseconds, made it difficult to confirm this hypothesis.”
Hoping to solve the mystery by catching some of these bursts in action at an unprecedented level of detail, Tsuchiya and Yuuki Wada, the study’s lead author, set up a series of three-sensor systems facing radio towers throughout Kanazawa City, Ishikawa Prefecture. By focusing their sensors on radio towers, the researchers hoped that whenever lightning strikes, the sensors would capture optical, radiofrequency, and high-energy radiation data during, before, and after the event.
Accelerating Electrons Near the Speed of Light
According to the published study, the research team successfully captured several TGF gamma-ray bursts during lightning storms. After examining the sensor data, they spotted a series of events that they believed resulted in the high-energy gamma-ray bursts.
Moments before the lightning struck, the team says its radiofrequency sensor detected a “downward negative leader” coming from the clouds toward the tower. The team’s optical sensor (camera) picked up a simultaneous “upward positive leader” of the lightning strike coming from the tower toward the cloud. Moments before the two leaders met, the team’s high-energy radiation sensor picked up the telltale signature of a TGF.
“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,” they explain.
After determining that this same series of detections occurred each time the team detected a TGF, they took a closer look at the data. Analysis of one event found that 31 microseconds before the two upward and downward leader streams met, they created a concentrated electrical field. Electrons trapped within this field were accelerated to near light speed, generating enough energy for a gamma ray burst. While it released significant energy, the burst was short-lived, terminating 20 microseconds after the two leaders joined to form a lightning bolt.
“Our results indicate that an immense number of electrons were produced and accelerated to relativistic energies in a strong and compact electric-field region between the two leaders,” the study authors write.
Improving the Safety and Resilience of Vulnerable Structures
The authors note that their work contributes critical data to solving the mystery of how lightning can generate high-energy TGFs. The study also offers scientific support to previous lighting leader dynamics theories and the role thermal runaway and relativistic feedback might play in these high-energy gamma ray bursts.
“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,” Wada explained.
From a more practical standpoint, the researchers believe understanding the association between TGFs could help improve the “safety and resilience” of buildings and other structures exposed to high-energy atmospheric phenomena. Such applications could become even more critical as extreme weather events due to the rise in global temperature continue to increase.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.