Gamma-ray flashes (TGFs) emitted from thunderstorms…..Credit: NASA
When thinking about particle physics, most people will think about laboratories and human-built devices, especially the monster atom smashers like the Tevatron or Large Hadron Collider. Well, it turns out nature beat us to it. The primal particle accelerator on Earth turns out to be the thunderstorm. Every day thunderstorms produce a variety of high-energy particles including gamma rays and antimatter. Yes, antimatter. This is something scientists have just discovered thanks to the NASA Fermi Gamma-ray Space Telescope.
The Fermi telescope spends much of its time scanning the distant galaxies, but the Fermi’s Gamma-ray Burst Monitor (GBM) can also turn its attention to Earth. It’s there, in our own front-yard so to speak, that it observed the peculiar waves of high-energy gamma-rays known as TGFs (Terrestrial Gamma Flashes) emanating from the tops of thunderstorms.
Scientists have known about TGFs for decades, although their origin remains only partially understood. Thunderstorms produce enormous electro-magnetic fields, tens of thousands of meters in size that accelerate particles to speeds near to that of light. Along the way the particles crash into the molecules of air and other material within the storm clouds, creating gamma-rays and now as it turns out, antimatter.
The Fermi GBM doesn’t actually see antimatter, which is destroyed almost simultaneously with its creation, but its counterpart to electrons in the world of matter – positrons. Electrons and positrons are collected in the magnetic fields of the Earth and in this case in the electric fields near the top of thunderstorms until they sometimes discharge in a gigantic flash with a signature yellowish color. It’s this color, which is picked up by the GBM on Fermi.
The importance of the discovery of antimatter in TGFs (along with the surprise) is that it opens an even more intriguing view into the physics of thunderstorms and the phenomena of lightning. There are many mysteries yet to be probed in the powerful display of particle physics within the big thunderstorm cells. Perhaps there are applications for theoretical models, or perhaps some speculation that the production of gamma-rays and positrons that shoot as beams from the tops of thunderstorms may be detectable elsewhere in the galaxy – like a signature of weather on other planets.
“The Fermi results put us a step closer to understanding how TGFs work,” said Steven Cummer at Duke University. “We still have to figure out what is special about these storms and the precise role lightning plays in the process.”