Researchers at Kyoto University have proved that lightning bolts work as natural particle accelerators, a new paper published in the journal Nature reports.
Scientists first suspected that lightning bolts could accelerate particles back in 1925, when they postulated that energized, radioactive particles could zip through a thunderstorm. However, they had no way to prove such a process existed. In the recent study, the team overcame that by discovering that lightning’s particles emit energy at precise wavelengths, which can be detected.
As lightning strikes, electrons speed between either two clouds, or a cloud and the Earth’s surface. However, those particles do not travel through empty space. Rather, they crash into multiple atmospheric gas molecules along the way. That then heats the gas into plasma, which glows with a type of electromagnetic radiation known as blackbody radiation.
Though humans can notice some of that glow, many emissions — such as X-rays and gamma-rays — take place at frequencies that cannot be detected by the human eye.
By using instruments to look at those beams of invisible energy, the team found that the rays excite ambient nitrogen and oxygen in the atmosphere. That then knocks out neutrons from the molecules they encounter and creates nuclear fission.
This works because of the molecules nitrogen-14 and oxygen-16. Both of those are stable and freely float around in the atmosphere. However, when the above process removes a neutron from each — creating nitrogen-13 and oxygen-15 — it causes them to become unstable. From there, they rapidly decay and fire off an additional neutrino and positron.
That then causes the neutrinos to stream away, while the positrons go on to collide with ambient electrons. That meeting of matter and antimatter culminates in a bright flash of energy, Live Science reports.
“Usually people think lightning can interact with electrons in atoms,” Teruaki Enoto, a researcher from Kyoto University, told ScienceAlert. “The photonuclear reactions indicate that lightning also interacts even with nuclei if gamma rays have sufficiently high energy to knock out neutrons from the nuclei.”
This research is important because, not only does it shed light on a new process, but it gives insight into potential uses for lightning. However, there are still many questions that still need to be answered. For instance, the photonuclear reaction, while interesting, does not appear to match an event scientists observed in 2009. It is also not yet clear how much of the isotope is produced in this way. The team hopes to continue monitoring the natural phenomena to see what else they can learn.