Lightning in the Eye of This Hurricane Shot a Beam of Antimatter Toward Earth

On October 23, 2015, Hurricane Patricia, the most powerful tropical cyclone ever recorded in the Western Hemisphere, slammed into Mexico's Pacific coast.

While the storm was at its peak intensity, a Hurricane Hunter aircraft operated by the National Oceanic and Atmospheric Administration (NOAA) flew through the eyewall. As it did so, an instrument on board the plane detected a phenomenon that has been predicted by scientists—but never observed before.

Now, the phenomenon has been reported in a new study published in Journal of Geophysical Research, which describes the detection of a downward beam of antimatter accompanied by a burst of powerful gamma-rays—very high frequency waves of electromagnetic radiation.

Antimatter describes a material that is the antiparticle to a corresponding particle of ordinary matter. The beam of antimatter detected in the hurricane, for example, was composed of positrons—the antiparticle of electrons. Such a phenomenon has never been seen before in this context, according the researchers, although its discovery was not unexpected.

"We report the first observation of gamma‐ray emission from lightning within a hurricane eyewall, consistent with production by a downward beam of positrons," they wrote in the study.

The beam of positrons was the downward component of something called a terrestrial gamma-ray flash (TGF), which sent a short blast of radiation upward into space, according to David Smith, a professor of physics at the University of California Santa Cruz and an author of the study.

TGFs themselves were first observed in 1994 by space-based instruments that look for gamma rays. They occur in conjunction with lightning and have since been detected thousands of times by satellites. Scientists have predicted, based on theoretical models, that these bright, upward-moving gamma-ray flashes should be accompanied by downward beams of positrons—but this phenomenon had never been detected until the latest discovery.

"This is the first confirmation of that theoretical prediction, and it shows that TGFs are piercing the atmosphere from top to bottom with high-energy radiation," Smith said in a statement. "This event could have been detected from space, like almost all the other reported TGFs, as an upward beam caused by an avalanche of electrons. We saw it from below because of a beam of antimatter (positrons) sent in the opposite direction."

So, how are these TGFs produced?

Strong electric fields in thunderstorms can accelerate electrons to near speed of light levels. These electrons collide and scatter off atoms in the atmosphere, emitting gamma-rays in the process. Sometimes they smash into other electrons in these atoms, accelerating them to the speed of light as well. TGFs are created when sufficient numbers of these accelerated electrons form a chain reaction.

However, scientists are still unsure about several aspects of the physics behind TGFs. "It's an extraordinary event, and we still don't understand how it gets so bright," Smith said.

On the other hand, the physical processes behind how antimatter is produced are better understood. Gamma-rays from a TGF interact with the nuclei—or center—of atoms, creating negatively charged electrons and positively charged positrons. Because they have opposite charges, they are accelerated in opposite directions by the electrical field of the thunderstorm: The positrons move downward, producing more gamma-rays and X-rays, while the electrons move upward.

"What we saw in the aircraft are the gamma-rays produced by the downward positron beam," Smith said.