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At any given moment about 18,000 thunderstorms are in progress somewhere on the globe. New
observations by NASA's Fermi Gamma-ray Space Telescope show that thunderstorms make antimatter.
The process starts with a terrestrial gamma-ray flash, or TGF; an intense pulse of gamma rays
originating from thunderstorms. These dots mark TGF's observed by Fermi's Gamma-ray Burst
Monitor during the spacecraft's first eight months of operations. Researchers estimate
that there may be as many as five hundred TGF's each day. On December 14, 2009, as Fermi
passed over Egypt, it spotted a TGF produced by a thunderstorm in Zambia The TGF was over
the spacecraft's horizon where Fermi couldn't see it. So how could Fermi have detected it?
Scientists believe that the TGF process begins with thunderstorm's intense electrical field.
Electrons within this field become accelerated upward above the storm where the air is thin;
the electrons can ramp up to speeds nearly as fast as the speed of light. When these
ultra-fast electrons encounter an atom, they emit gamma rays. Very rarely, one of these
gamma-ray photons grazes an atom and transforms into a pair of particles. One, an electron,
is normal matter; the other is antimatter, the electron's opposite, called a positron.
The gamma rays travel in straight lines, but the charged particles spiral along lines of
Earth's magnetic field. And that was the route to Fermi. The particles created by the TGF
rode upwards on magentic field lines and then struck the spacecraft. The positrons annihilated
when they struck electrons in Fermi creating a flash of gamma rays. For an instant Fermi
became a gamma-ray source and set off its own detectors. A fraction of a second later,
some of the particles were bounced back along the same magnetic field line. They again passed
through Fermi and again produced gamma rays. The spacecraft has observed this phenomenon
in at least four other occasions. So the next time lightning flashes and thunder roars remember
-- you may be witnessing antimatter in the making.