Ordinary people know Gamma Rays because of the superhero Hulk. But scientists have known him for a long time. Gamma rays are the most energetic light waves produced in the universe. So energetic, that they are seen in certain radioactive decays, in many cosmic explosions, and also in thunder and lightning.
Terrestrial Gamma-ray flashes (TGF) are produced by bremsstrahlung, a German word which when translated means 'braking radiation', referring to an accelerated or decelerated electrically charged particle that emits electromagnetic radiation. In the case of TGF, the cause is the accelerated electrons.
In the new paper, which is currently available on ArXiv, the researchers report on recent observations from the optical partner of TGF. This is important because the two main hypotheses for the production of gamma rays by lightning produce different signatures in visible light.
The first is the Relativistic FeeDback (RFD) mechanism, which shows that photons (particles of light) and positrons (the antimatter equivalent of electrons), generate feedback that produces an avalanche of electrons.
Antimatter in thunderclouds occurs so this scenario should be taken seriously. If this model is correct, there should be very little or no sign in visible light and very little ultraviolet light. This is known as dark lightning.
An alternative explanation is, a thermal runaway electron production mechanism, in which a local high electric field will generate a cascade of electrons. This field will be ten times higher than the conventional damage field.
"The thermal runaway electron production mechanism assumes that TGF events are produced around the ends of the lightning-associated band. The free electron population is then further accelerated in a decrease in potential in front of the lightning tip to the escaping electrons via the thermal escape mechanism," the authors of the paper said. the.
Thermal runaway will produce optical signals simultaneously with gamma rays. And during a thunderstorm on September 11, 2021, the researchers used the Telescope Array Surface Detector (TASD), which detects gamma rays and optical signals from thunderstorms, consistent with a thermal runaway production mechanism.
"Our data show a substantial increase in visible light in correlation with TGF production. From these results it seems reasonable to conclude that our results support the model of the thermal escape mechanism and do not support the idea that TGF is a dark event as proposed by the Relativistic Feedback mechanism," write the author in the conclusion of the study.
This is not the end of the story about gamma rays emanating from lightning, it is far from it. Scientists today are just scratching the surface of the complexity of thunderstorms and lightning. Further study of these findings will certainly be of interest.