NASA's Fermi Catches Thunderstorms Hurling Antimatter into Space
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Scientists using NASA's Fermi Gamma-ray Space Telescope have detected beams of antimatter produced above thunderstorms on Earth, a phenomenon never seen before...
Scientists using NASA's Fermi Gamma-ray Space Telescope have detected beams of
antimatter produced above thunderstorms on Earth, a phenomenon never seen
before.
Scientists think the antimatter particles were formed in a
terrestrial gamma-ray flash (TGF), a brief burst produced inside thunderstorms
and shown to be associated with lightning. It is estimated that about 500 TGFs
occur daily worldwide, but most go undetected.
"These signals are the
first direct evidence that thunderstorms make antimatter particle beams," said
Michael Briggs, a member of Fermi's Gamma-ray Burst Monitor (GBM) team at the
University of Alabama in Huntsville (UAH). He presented the findings Monday,
during a news briefing at the American Astronomical Society meeting in
Seattle.
Fermi is designed to monitor gamma rays, the highest energy form of light. When
antimatter striking Fermi collides with a particle of normal matter, both
particles immediately are annihilated and transformed into gamma rays. The GBM
has detected gamma rays with energies of 511,000 electron volts, a signal
indicating an electron has met its antimatter counterpart, a
positron.
Although Fermi's GBM is designed to observe high-energy events
in the universe, it's also providing valuable insights into this strange
phenomenon. The GBM constantly monitors the entire celestial sky above and the
Earth below. The GBM team has identified 130 TGFs since Fermi's launch in
2008.
"In orbit for less than three years, the Fermi mission has proven
to be an amazing tool to probe the universe. Now we learn that it can discover
mysteries much, much closer to home," said Ilana Harrus, Fermi program scientist
at NASA Headquarters in Washington.
The spacecraft was located immediately above a thunderstorm for most of the
observed TGFs, but in four cases, storms were far from Fermi. In addition,
lightning-generated radio signals detected by a global monitoring network
indicated the only lightning at the time was hundreds or more miles away. During
one TGF, which occurred on Dec. 14, 2009, Fermi was located over Egypt. But 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.
"Even though Fermi couldn't see the storm, the spacecraft
nevertheless was magnetically connected to it," said Joseph Dwyer at the Florida
Institute of Technology in Melbourne, Fla. "The TGF produced high-speed
electrons and positrons, which then rode up Earth's magnetic field to strike the
spacecraft."
The beam continued past Fermi, reached a location, known as
a mirror point, where its motion was reversed, and then hit the spacecraft a
second time just 23 milliseconds later. Each time, positrons in the beam
collided with electrons in the spacecraft. The particles annihilated each other,
emitting gamma rays detected by Fermi's GBM.
Scientists long have suspected TGFs arise from the strong electric fields near
the tops of thunderstorms. Under the right conditions, they 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.
But the cascading electrons produce so many gamma rays that
they blast electrons and positrons clear out of the atmosphere. This happens
when the gamma-ray energy transforms into a pair of particles: an electron and a
positron. It's these particles that reach Fermi's orbit.
The detection of positrons shows many high-energy particles are being ejected from the atmosphere. In fact, scientists now think that all TGFs emit electron/positron beams. A paper on the findings has been accepted for publication in Geophysical Research Letters.
NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership. It is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. It 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.
The GBM Instrument Operations Center is located at the National Space Science Technology Center in Huntsville, Ala. The team includes a collaboration of scientists from UAH, NASA's Marshall Space Flight Center in Huntsville, the Max Planck Institute for Extraterrestrial Physics in Germany and other institutions.
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