"These signals are the first direct evidence that thunderstorms make antimatter particle beams," said Michael Briggs, a university researcher whose team, located at UAHuntsville, includes scientists from NASA Marshall Space Flight Center, the University of Alabama in Huntsville, Max-Planck Institute in Garching, Germany, and from around the world. He presented the findings during a news briefing at the American Astronomical Society meeting in Seattle.
Scientists think the antimatter particles are formed in a terrestrial gamma-ray flash (TGF), a brief burst produced inside thunderstorms that has a relationship to lighting that is not fully understood. As many as 500 TGFs may occur daily worldwide, but most go undetected.
The spacecraft, known as Fermi, is designed to observe gamma-ray sources in space, emitters of the highest energy form of light. Fermi’s GBM constantly monitors the entire celestial sky, with sensors observing in all directions, including some toward the Earth, thereby providing valuable insight into this strange phenomenon.
When the antimatter produced in a terrestrial thunderstorm collides with normal matter, such as the spacecraft itself, both the matter and antimatter particles immediately are annihilated and transformed into gamma-rays observed by the GBM sensors. The detection of gamma-rays with energies of a particular energy -- 511,000 electron volts -- is the smoking-gun, indicating that the source of the observed gamma-rays in these events is the annihilation of an electron with its antimatter counterpart, a positron, produced in the TGF.
Since the spacecraft’s launch in 2008, the GBM team has identified 130 TGFs, which are usually accompanied by thunderstorms located directly below the spacecraft at the time of detection. However, in four cases, storms were a far distance from Fermi. Lightning-generated radio signals, detected by a global monitoring network, indicated the only lightning at the time of these events was hundreds or more miles away.
During one TGF, which occurred on December 14, 2009, Fermi was located over Egypt. However, the active storm was in Zambia, some 2,800 miles to the south. The distant storm was below Fermi’s horizon, so any gamma-rays it produced could not have been detected directly. Although Fermi could not see the storm from its position in orbit, it was still connected to it through sharing of a common magnetic field line of the Earth, which could be followed by the high-speed electrons and positrons produced by the TGF. These particles travelled up along the Earth’s magnetic field lines and struck the spacecraft. The beam continued past Fermi along the magnetic field, to a location known as a mirror point, where its motion was reversed, and then 23 milliseconds later, hit the spacecraft again. Each time, positrons in the beam collided with electrons in the spacecraft, annihilating each other, and emitting gamma-rays detected by Fermi’s GBM.
NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership. The spacecraft is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. The GBM instrument is a collaboration between scientists at NASA's Marshall Space Flight Center, the University of Alabama in Huntsville, and the Max-Planck Institute in Garching, Germany. The Fermi mission was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.
Ray Garner | Newswise Science News
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