We do, however, know that it’s extremely energetic – and a new study has confirmed that it’s powerful enough to occasionally create nuclear reactions in the sky.
“Lightning and thunderclouds are natural particle accelerators”, the team surmises rather beautifully in their Nature paper. This was known to involve “avalanches of... runaway electrons”, but now it seems it involves things as kooky as antimatter antiparticles.
Nuclear reactions aren’t easy to induce. They’re generally considered to define the moment in which two nuclei or a nucleus and a subatomic particle collide, creating different atomic products as a result. They need a lot of energy – say, for example, the interaction of cosmic rays with our planet’s atmosphere.
The average lightning bolt involves the transfer of at least one billion joules of energy, give or take, and it’s long been suspected that the most energetic flashes would be sufficient to create nuclear reactions too. The idea is that their electrons can occasionally produce gamma rays, which are powerful enough to break up nuclei flitting around up there.
This type of reaction would produce neutrinos, neutrons and even antimatter for the briefest of moments. These signals have been detected by observatories and detectors all across the planet for almost four decades now, but it’s been hard to confirm that they’re being made by lightning.
In order to solve this mystery once and for all, a team of Japanese astrophysicists led by Kyoto University decided to hook their instrumentation up to a series of radiation detectors installed at a nuclear power plant in Niigata. They hoped to directly link these nuclear reactions to lightning strikes – and they weren’t disappointed.
This February, a potent thunderstorm brewed in the Sea of Japan, just offshore. Not only did they pick up on high levels of gamma radiation matching several lightning strikes, but they also picked up on very specific energy signatures that followed on shortly thereafter.
These signatures could only be matched to one very specific set of situations. Unstable carbon, nitrogen and oxygen isotopes were being produced by gamma ray interactions. They then naturally emitted neutrons, neutrinos and antimatter poistrons. This antimatter was then quickly and explosively annihilated upon making contact with electrons.
This study provides the first unequivocal evidence that lightning can generate nuclear reactions within our atmosphere. Perhaps more importantly – after cosmic ray interactions and nuclear reactions within the hearts of stars – it’s now known to be the third natural process in which these reactions occur.