NASA'S Fermi Catches Thunderstorms Hurling Antimatter Into Space
WASHINGTON -- 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.
"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."
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.
For more Fermi information, images and animations, visit:
http://www.nasa.gov/fermi
Source: NASA
