Sino-Japanese team in gamma ray breakthrough
Print Edition
A JOINT research team made up of Chinese and Japanese scientists at an observatory in Tibet has discovered the highest-energy cosmic gamma rays ever observed, opening a new window to explore the extreme universe.
The energy of the gamma rays is as high as 450 TeV 鈥 equivalent to 45 billion times the energy of a medical X-ray, researchers from the Institute of High Energy Physics of the Chinese Academy of Sciences told reporters yesterday.
Scientists believe that those energetic gamma rays were from the Crab Nebula, a famous supernova remnant in the constellation Taurus, about 6,500 light years away from Earth.
Previously, the highest energy ever observed for a gamma-ray photon was 75 TeV, which was detected by the HEGRA Cherenkov telescope in Germany.
鈥淏efore this discovery, many scientists believed that photons could not be accelerated to energy higher than 100 TeV,鈥 said Huang Jing, a researcher from IHEP and the co-spokesperson for the experiment.
鈥淭he discovery is a milestone in the search for the origin of the mysterious cosmic rays,鈥 said Professor Chen Yang, an expert on supernova remnants from Nanjing University.
Scientists believe the rays were created in four steps: First, the electrons accelerated up to PeV (1,000 trillion electron volts) in the nebula.
Then the PeV electrons interacted with the cosmic microwave background radiation, the remnant radiation from the Big Bang filling the whole universe.
And then a CMBR photon was kicked up to 450 TeV by a PeV electron.
The researchers thus conclude that the Crab Nebula is the most powerful natural electron accelerator known in our Galaxy.
The Crab Nebula was produced by a supernova explosion in 1054, which was recorded in official documents of the Northern Song Dynasty (960-1127).
In 1969, scientists discovered a pulsar, rotating 30 times per second, embedded in the nebula. The Crab Nebula has since been observed at all electromagnetic wavelengths ranging from radio to very high energy gamma rays.
The observatory, in Yangbajing Town in the Tibet Autonomous Region at 4,300 meters above sea level, was operated jointly by China and Japan in
1990.
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