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by Dr. Tony Phillips
January 11,
2011
from
Science.NASA Website
An artist's concept of antimatter
spraying above a thunderhead.
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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. |
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.
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.
The three steps
thunderstorms must take
to
produce bursts of anti-matter.
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."
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