Researchers observe gamma-ray burst on Earth for the first time
Gamma-ray bursts do not only occur in space, but also on Earth. Researchers from Japan have observed their formation during a thunderstorm for the first time.
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Gamma-ray bursts normally occur in space, for example when a star explodes. Such a gamma-ray burst releases more energy in seconds than the sun does during its entire lifetime. Gamma-ray bursts – although much less energetic – also occur on Earth. Researchers from Japan claim to have observed one for the first time.
Terrestrial gamma-ray flashes (TGF) are bursts of high-energy gamma radiation in the Earth's atmosphere. They were first discovered in the mid-1990s by a space probe orbiting the Earth. 30 years later, researchers from Osaka University in Japan observed a TGF and described its formation in the journal Science Advances.
The team led by Yuuki Wada set up a structure with different sensors on two television towers in Kanazawa to observe TGFs. The sensors can detect a broad spectrum of radiation, from radio waves to visible light and gamma radiation.
On January 30, the sensors detected a lightning strike in one of the towers. A lightning strike creates two discharge paths: a negatively charged one from the cloud towards the ground and a positively charged one from the ground upwards. When they meet, a discharge occurs.
The gamma-ray burst lasted 20 microseconds
In this particular flash, the discharge, which had a current of 56 kiloamperes, took place at an altitude of just under one kilometer. The gamma flash occurred fractions before the discharge paths met: 31 microseconds before the sensors detected the first gamma radiation. The entire TGF lasted around 20 microseconds.
“The multisensor observations made here are a world first,” said senior author Harufumi Tsuchiya. “Although some mysteries remain, this technique has brought us closer to understanding the mechanism of these fascinating bursts of radiation.” They provide important clues as to how lightning generates enough energy to produce gamma rays.
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The first TGFs were observed from space, as satellites cover a large area and gamma rays are not absorbed. However, these observations are imprecise. Last year, two papers were published in the journal Nature – here and here –, in which the authors described gamma-ray bursts in tropical thunderstorms. They made their observations from a modified spy plane, which they flew into the thunderstorm systems.
“The recent Nature articles are based on observations from the air,” lead author Wada told the US online magazine Gizmodo. “They are also very interesting, but ground-based observations can be done much more cost-effectively.”
(wpl)
