美國航太總署發現 雷電風暴釋放出反物質 - 地球科學討論

http://e-info.org.tw/node/63057

摘譯自2011年1月18日美國，阿拉巴馬州報導；張桂芳編譯；蔡麗伶審校

科學家利用美國國家航空暨太空總署的費米伽瑪射線太空望遠鏡（NASA's Fermi
Gamma-ray Space Telescope）在雷電風暴上方發現反物質束，締造首次地球上，反物質
在自然狀態下出現的記錄。

科學家認為反物質粒子是在雷暴圈内形成，閃電時地球高層大氣中的伽瑪射線閃光中。根
據他們的估計，全球各地每天約出現500次伽瑪射線閃光，但大多數探測不到。

任職於亨茨維爾，阿拉巴馬大學費米伽瑪射線爆發監控小組成員邁克爾.布里格斯表示：
「這些信號是證明雷暴會產生反物質粒子束的第一個直接證據。」他上週在西雅圖召開的
美國天文學會會議上公佈了該小組的調查結果。

太陽耀斑在爆發過程中製造出反物質。在地球所在的銀河系中曾觀測到反物質雲，但這種
現象從未出現在地球上。

如同巨大的粒子加速器，雷暴可以噴發地面伽瑪射線閃光，稱為 TGFs，以及高能量的電
子和正電子。正電子是電子的反粒子。

於2008年6月11日升空的美國國家航空暨太空總署的費米伽瑪射線太空望遠鏡，其目的為
從距離地球上空350英里的軌道上，觀測光的最高能量形式伽瑪射線。

雖然費米伽瑪射線爆發顯示器設計用於觀察宇宙中的高能事件，同時還讓科學家對反物質
現象有更深的認識。

伽瑪射線爆發監視器每90分鐘環繞地球一圈，不斷監測整個地球上空。自費米太空望遠鏡
發射至今，伽瑪射線爆發監控小組已辨識出130個地面伽瑪射線閃光。

科學家長期以來一直懷疑，地面伽瑪射線閃光發生在雷暴頂部附近的強大電場。他們表示
，在適當條件下，該電場強到足以將大量電子向上推升，釋放出像雪崩般巨大的能量。

當前述高能量電子受到空氣分子阻力偏折而釋放出伽瑪射線，其速度幾乎可近光速。

通常這些被測到的伽瑪射線為地面伽瑪射線閃光。但如瀑布般噴瀉而出的電子，釋放出大
量的伽馬射線，讓電子和正電子遠遠爆噴出大氣層。這種狀況發生在當伽瑪射線的能量轉
換成一對粒子：一個電子和一個正電子的時候，而這些正是出現在地球上空350英里費米
軌道上的粒子。

觀測到正電子意味著許多高能量粒子衝出大氣層外。事實上科學家現在認為，所有TGFs皆
釋放出電子 /正電子束。這些研究結果的論文已被接受並刊登在「地球物理研究通訊。」

Thunderstorms Emit Beams of Antimatter, NASA Discovers
HUNTSVILLE, Alabama, January 18, 2011 (ENS)

For the first time, antimatter has been observed occurring naturally on
Earth, as scientists using NASA's Fermi Gamma-ray Space Telescope have
documented beams of antimatter produced above thunderstorms.

The scientists think the antimatter particles are formed inside thunderstorms
in terrestrial gamma-ray flashes associated with lightning. They estimate
that about 500 gamma-ray flashes 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 team at the University of Alabama in Huntsville. He
presented the team's findings last week at the American Astronomical Society
meeting in Seattle.

Antimatter is created in solar flares on the Sun and clouds of antimatter
have been observed in the Milky Way, our home galaxy, but the phenomenon has
never before been seen on Earth.

Acting like enormous particle accelerators, thunderstorms can emit
terrestrial gamma-ray flashes, called TGFs, as well as high-energy electrons
and positrons, which are the antiparticles of electrons.

Launched June 11, 2008, NASA's Fermi Gamma-ray space telescope is designed to
monitor gamma rays, the highest energy form of light, from its orbit 350
miles above the Earth.

Although Fermi's Gamma-ray Burst Monitor is designed to observe high-energy
events in the universe, it also provides insights into the antimatter
phenomenon.

The Gamma-ray Burst Monitor constantly monitors the entire sky, circling the
Earth every 90 minutes. The Gamma-ray Burst Monitor team has identified 130
terrestrial gamma-ray flashes since the Fermi space telescope was launched.

Scientists long have suspected terrestrial gamma-ray flashes 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 deflected by air molecules.

Normally, these gamma rays are detected as a terrestrial gamma-ray flash. But
the cascading electrons produce so many gamma rays that they blast electrons
and positrons clear of the atmosphere. This happens when the gamma-ray energy
transforms into a pair of particles: an electron and a positron. It is these
particles that reach Fermi's orbit 350 miles above the Earth.

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 these findings has been accepted for
publication in the journal "Geophysical Research Letters."

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