By far the thing that made me double-take today was what sounded like an off-hand comment from invited speaker Dr. Julie E. McEnery. She listed out the types of gamma ray events that Fermi (a satellite observatory) was detecting, and on that list was thunderstorms. On Earth.
Luckily she went on in more detail, but I was left with the feeling that I had missed something back in Astro 179. Why did I have the impression that gamma rays from thunderstorms was NEWS?
Fermi is a space telescope, designed to view the universe at high-energy wavelengths – gamma rays, x-rays and the like. Fermi was originally called GLAST, if you remember learning about it at the beginning of its mission.
Gamma Ray Bursts
Gamma rays are a type of light, a much higher-energy type of light than visible light – like ultraviolet only more “ultra.” Gamma Ray Bursts (or GRBs) are exactly what they sound like: bursts or flashes of gamma ray light. For a good while there after they were first discovered they were one of the great unsolved mysteries of the universe.
A lot of the mystery was because GRBs were so fast, we couldn’t turn our telescopes to focus on them before they were mostly over. Although many mysteries about GRBs remain, there are two basic known causes: merging neutron stars, and supernovae of extremely massive stars. It is also widely accepted that GRBs take place in extremely distant galaxies, not nearby.
Thunderstorms and TGFs
Gamma-rays produced on Earth, or “Terrestrial Gamma-ray Flashes” (TGFs), are a phenomenon currently being studied (and I thought this was new news, oops!). According to NASA’s press release, about 500 TGFs occur every day, but we don’t detect most of them. TGFs are usually associated with lightning.
Under the right conditions, [scientists] say, the field becomes strong enough that it drives an upward avalanche of electrons. Reaching speeds nearly as fast as light, the high-energy electrons give off gamma rays when they’re deflected by air molecules. Normally, these gamma rays are detected as a TGF.
-NASA Press Release
So, Fermi makes it possible to study these gamma-ray flashes within thunderstorms. And Fermi has detected over 130 TGFs. Who knew?
The Plot Thickens – Antimatter
If the gamma-ray flashes in thunderstorms aren’t the news – what is? Well, in addition to the detection of the gamma-rays, Fermi detected a beam of antimatter particles being shot out the top of the thunderstorm – positrons, to be specific.
When the “avalanche” of electrons is driven upwards creating gamma rays, it also starts off a cascade effect where some of the gamma rays transform into a pair of particles: an electron and a positron. These pairs of particles are blasted out of the atmosphere by the sheer amount of energy going on in these reactions. This “beam” of matter and antimatter (electrons and positrons) was detected by Fermi.
How’s that for dinner table conversation? “Did you know that thunderstorms make antimatter?” There’s even more to this story, but this article is dense enough for today. I’ll refer you to the links below to hear Chapter 2.
~ A l i c e !