Thunderstorms Make Antimatter
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Jan. 11, 2011: 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 inside thunderstorms in
a terrestrial gamma-ray flash (TGF) 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.
Fermi was above Egypt on Dec. 14, 2009, when a burst of positrons emerged from an
African thunderstorm. CLICK HERE TO VIEW A LARGER IMAGE
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.
Click to view the three steps thunderstorms must take to produce bursts of anti-matter.[more]
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.
"The Fermi results put us a step closer to understanding how TGFs work," said
Steven Cummer at Duke University. "We still have to figure out what is special
about these storms and the precise role lightning plays in the process."
Editor: Dr.
Tony Phillips | Credit: Science@NASA
| More Information |
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Fermi Home
Page -- from NASA
Are
TGFs Hazardous to Air Travelers? --- Science@NASA
Firefly
Mission to Study Terrestrial Gamma-ray Flashes -- (Science@NASA)
What
NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle Comes Out of the Top of a Thunderstorm? -- (Science@NASA) 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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