The Institute of High Energy Physics of the Chinese Academy of Sciences announced on the 17th that the national major scientific and technological infrastructure "High Altitude Cosmic Ray Observatory "Lasso" (LHAASO)" recorded 1400 trillion electron volts (1.4PeV) of gamma photons, which is the highest energy photon observed by humans so far, which will help further unlock the mystery of cosmic rays.
In this regard, Carl Zemeris, editor-in-chief of the physical sciences of Nature, commented that these exciting discoveries, although still preliminary, were made possible by the observation of the partially completed "lasso". In the future, after the completion of the "lasso", I believe that more such gamma sources will be found. These findings bring us one step closer to understanding the origin of high-energy cosmic rays.
What is a cosmic ray?
Cosmic rays are high-energy charged particles in interstellar space, discovered in 1912 by Austrian physicist Victor Hess, who was also awarded the 1936 Nobel Prize in Physics. About 90 percent of the cosmic ray particles detected are protons, 9 percent are helium nuclei, and heavier nuclei and other particles such as electrons make up the remaining 1 percent.
In the interstellar space of the Milky Way, cosmic rays contribute 1/3 of the energy density, are an important part of interstellar space, and dominate astrophysical processes such as interstellar chemistry and star formation. Therefore, the study of cosmic rays is of great significance for human understanding of the universe.
For current human civilization, 1PeV is an unattainable energy, compared to the current largest artificial particle accelerator on Earth (that is, cernion LHC) can accelerate particles at a limit of only about 0.01PeV. The origin of these cosmic rays is equivalent to a natural particle physics laboratory, and finding these objects and studying their properties is not only an important milestone in human understanding of the universe, but may also be a key step in breaking through the current framework of basic physics.
Milestone new discoveries
The origin of cosmic rays is a cutting-edge scientific question. Previous observations have not found any objects in the Milky Way that accelerate cosmic rays above 1PeV. In early April this year, the Institute of High Energy Physics of the Chinese Academy of Sciences announced that the ASγ experiment in Tibet observed ultra-high-energy gamma rays with a maximum energy of 957 trillion electron volts, very close to 1P.
Cao Zhen, a researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences, introduced that his team found photons with an energy of more than 1PeV from the very active star-forming region in the constellation Cygnus, in addition to finding 12 stable gamma ray sources, and the radiation energy extended to near 1PeV.
"This suggests that there are a large number of 'Beat Electron Volts' (PeVatron) in the Milky Way that can accelerate cosmic rays to 1PeV, which are candidates for ultra-high-energy cosmic ray sources, which is an important step toward solving the scientific problem of cosmic ray origin." Cao Zhen said.
According to reports, the discovery shows that young massive star clusters, supernova remnants, pulsar storm clouds, etc., are the best candidate objects for the origin of the ultra-high-energy cosmic rays in the Milky Way. At the same time, the discovery also requires scientists to re-understand the production and propagation mechanism of high-energy particles in the Milky Way, explore extreme celestial phenomena and their related physical processes, and test basic physical laws under extreme conditions.
The high-altitude cosmic ray observatory is located in Haizi Mountain, 4410 meters above sea level in Daocheng County, Sichuan Province, and is still under construction. The results of this report are based on observations from 1/2 of the built-up 1/2-scale detection device for 11 months in 2020. The research results were published in the internationally renowned academic journal Nature on the 17th.
China is expected to lead the world in cosmic ray research
China's cosmic ray experimental research has gone through three stages, and the cable currently under construction is the third generation of alpine cosmic ray laboratory.
High-altitude cosmic ray observatory "Lasso"
Cao Zhen said that alpine experiments can make full use of the atmosphere as a detection medium to observe on the ground, and the scale of the detector can be much larger than that of space-based detectors outside the atmosphere. For ultra-high-energy cosmic rays, this is the only means of observation.
The main project of Lasso began construction in 2017, and in April 2019, it completed 1/4 of the scale construction and put it into scientific operation, while building and running. In January 2020, 1/2 of the scale of construction was completed and put into operation, and in December of the same year, 3/4 of the scale was completed and put into operation. It is expected that all will be completed by the end of 2021.
Researcher He Huihai believes that the biggest innovation of the cable project is the combination of several detection technologies. "Previously, in the field of cosmic ray research, a detection technique was generally used for an experiment. The disadvantage of this single detection technique is that only one thing can be measured. In the cable experiment, we put 4 detectors together to measure the same case, and after measuring, we synthesized all the variables and analyzed them to make very fine measurements. ”
In addition, Lasso has developed a long-range clock synchronization technology that ensures that each detector throughout the array is synchronized to the sub-nanosecond level. At the same time, For the first time, Lasso also used advanced detection technologies such as silicon photocells and ultra-large photosensitive area microchannel plates photomultiplier tubes on a large scale, which greatly improved the spatial resolution of gamma ray measurements, enabling human beings to reach an unprecedented level in exploring deeper universes and higher energy rays.
At present, the project has been highly concerned and recognized by international peers, scientists in Russia, Switzerland, Poland and other countries hope to move the equipment here, and some international representative experimental groups have also expressed their desire for cooperation and joint observation. After the completion of the cable, China is expected to achieve a global leader in the field of cosmic ray research. Cao Zhen said.
Source: China Science Popularization Network Comprehensive report from Xinhua News Agency, People's Daily, Science and Technology Daily, etc
Editor: Wu Tong
Review: Wang Fei
Final Judge: Chen Lei
Image source: Institute of High Energy, Chinese Academy of Sciences
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