[Explanation] The origin of high-energy cosmic rays is an unsolved mystery for a century.
Recently, the China-Japan cooperation Tibet ASγ experiment observed the highest energy diffuse gamma-ray radiation so far, and it is diffusely distributed on the silver disk (the projection of the Milky Way in the sky).
This result has also become a milestone in the research on the origin of cosmic rays in the past century.
[Explanation] Cosmic rays are a stream of high-energy particles from cosmic space, and celestial bodies that can accelerate cosmic rays to PeV (electron volts) energy are also called "electron volt cosmic ray accelerators", but so far none of them have Observation confirmed.
The main difficulty is that the moving direction of the high-energy cosmic ray particles in the Milky Way will be deflected by the magnetic field, so they cannot search for the direction of their origin.
However, the high-energy gamma rays that can be generated when high-energy cosmic rays propagate can "point out the direction" for scientists.
[Concurrent] Huang Jing, researcher of the Center for Particle and Astronomy, Institute of High Energy Physics, Chinese Academy of Sciences
The Milky Way galaxy is full of magnetic fields, and these cosmic rays are charged particles. When deflected in the magnetic field, they lose the direction of their original source.
The direction we observe when we reach the earth is no longer the direction of the source.
But there is a kind of particle called gamma ray, which is a neutral particle that will not be deflected by the influence of a magnetic field.
Isn’t the direction it reverses the direction of the source?
Therefore, the study of gamma rays is also used as a good method to find the corresponding celestial bodies (the source of ultra-high energy cosmic rays).
[Explanation] To this end, the Chinese and Japanese teams cooperated with Tibet's Yangbajing International Cosmic Ray Observatory to carry out the Tibet ASγ experiment, using the self-developed innovative underground Muzi detector to carry out detection.
[Concurrent] Huang Jing, researcher of the Center for Particle and Astronomy, Institute of High Energy Physics, Chinese Academy of Sciences
Gamma rays are submerged in the vast "ocean" of cosmic rays. "Finding a needle in a haystack" is very difficult.
The previous detectors were not sensitive enough, and it was difficult to eliminate a large amount of cosmic ray background.
So we thought about whether we could invent a detector with a 2.5-meter-deep soil layer on top and a water Cherenkov muzi detector below the soil layer. It can be easily understood as a large pond with a large photoelectric. Multiplier tube.
This detector acts as a funnel, eliminating a large number of unwanted cosmic rays and picking out pure gamma rays.
[Explanation] After detection, the Tibet ASγ experiment found ultra-high-energy diffuse gamma rays on the silver disk, which is like a series of "footprints" left by the "electron-photovoltaic cosmic ray accelerator" in the Milky Way. Important evidence of the Milky Way.
[Concurrent] Huang Jing, researcher of the Center for Particle and Astronomy, Institute of High Energy Physics, Chinese Academy of Sciences
Our lives (cosmic rays) are also applied in every aspect, so we look for the origin of cosmic rays, also to discover the laws in nature, and to promote humans' understanding of nature.
This is the first time in the world that the "electron-photovoltaic cosmic ray accelerator" has actually been found in the Milky Way galaxy, and it is still pervading the silver disk.
This major discovery also laid a good foundation for the next step in exploring the origin and distribution of cosmic rays.
Cheng Yu reports from Beijing
Editor in charge: [Wang Kai]