Chinanews.com, Beijing, May 17 (Reporter Sun Zifa) The first batch of ultra-high energy cosmic accelerators were discovered in the Milky Way, and recorded a maximum of 1.4 beats (1 beat = 1 quadrillion) electron volts (electron volts) gamma photons. It is the highest-energy photon that humans have observed, which has changed humans’ traditional perception of particle acceleration in the Milky Way.
Relying on the two major scientific discoveries of the first batch of "electron volt accelerators" and the highest energy photon so far, the Institute of High Energy Physics, Chinese Academy of Sciences (Institute of High Energy, Chinese Academy of Sciences) was built in Daocheng, Sichuan, a major national scientific and technological infrastructure-high altitude cosmic rays The Observatory (LHAASO) officially opened the era of "ultra-high energy gamma astronomy", taking a crucial step towards solving the scientific problem of the origin of cosmic rays.
Logo of the High Altitude Cosmic Ray Observatory (LHAASO).
Photo courtesy of Institute of High Energy, Chinese Academy of Sciences
The Institute of High Energy of the Chinese Academy of Sciences and Springer Nature jointly held a press conference in Beijing on May 17 to introduce that the two major scientific discoveries in the field of high energy and astronomy were completed by the LHAASO International Cooperation Group led by the Institute of High Energy of the Chinese Academy of Sciences. The well-known academic journal "Nature" will be published online on the same day.
What is the specific content of LHAASO's new discovery?
The chief scientist of LHAASO and researcher Cao Zhen from the Institute of High Energy Research of the Chinese Academy of Sciences said that at present, LHAASO is still under construction. The two new scientific discoveries are based on the 1/2-scale detection device that LHAASO has built. Observation results.
The scientists of the LHAASO International Cooperation Group discovered that the photons with energies exceeding the beat electron volts came from the very active star-forming region in the Milky Way Cygnus.
The interior of the LHAASO water Cherenkov probe after the pool is filled with water.
Photo courtesy of Institute of High Energy, Chinese Academy of Sciences
At the same time, scientists also discovered 12 stable gamma-ray sources with energy extending to around 1 beat of electron volts. These are the brightest batch of gamma-ray sources in the Milky Way within the field of view of LHAASO. The measured gamma photon signal Higher than 7 times the standard deviation of the surrounding background, the measurement accuracy of the source position is better than 0.3 degrees.
Part of the detector array installed in the LHAASO pool.
Photo courtesy of Institute of High Energy, Chinese Academy of Sciences
Although the data accumulated in this observation is still very limited, all sources that can be observed by LHAASO have gamma radiation above 0.1 PeV, also called "ultra-high energy gamma radiation."
This shows that the galaxy is full of electron volt accelerators, and the largest accelerator built by mankind on the earth (the Large Hadron Collider at the European Nuclear Research Center) can only accelerate particles to 0.01 electron volts.
Why choose Cygnus?
Cao Zhen said that the Cygnus star-forming region has many star clusters with a large number of massive stars. The lifespan of massive stars is only on the order of a million years. Therefore, the star clusters are filled with a large number of violent activities of the life and death of stars, which have complex and strong activities. The shock wave environment is an ideal place for acceleration of cosmic rays and is called the "Particle Astrophysics Laboratory".
A detector array at LHAASO after snow.
Photo courtesy of Institute of High Energy, Chinese Academy of Sciences
Why is it said that a new era of "ultra-high energy gamma astronomy" is opened?
Cao Zhen pointed out that the existence of the energy limit of the cosmic ray accelerator in the Milky Way was previously "common knowledge", so that the predicted gamma-ray energy spectrum is "truncated" above 0.1 beat electron volts, and the new discovery of LHAASO completely breaks this "limit." ", most sources are not truncated.
Therefore, these discoveries officially opened the era of "super-high energy gamma astronomy" observations, indicating that young massive star clusters, supernova remnants, pulsar wind and clouds, etc. are the best candidates for the origin of ultra-high energy cosmic rays in the Milky Way, and will help to decipher the cosmic rays. The origin of this "mystery of the century".
He said that on the basis of LHAASO’s new discoveries, scientists also need to re-understand the production and propagation mechanisms of high-energy particles in the Milky Way, explore extreme celestial phenomena and related physical processes, and test basic physical laws under extreme conditions.
The scientific discovery of LHAASO is a milestone in the research process of the origin of cosmic rays, which can be summarized as three scientific breakthroughs:
The first is to reveal that cosmic accelerators capable of accelerating particle energy beyond 1 PeV are widespread in the Milky Way, breaking through the current popular theoretical models.
LHAASO discovered a large number of PeV cosmic acceleration sources in the Milky Way, and they are all candidates for ultra-high energy cosmic ray sources.
Second, with the establishment of LHAASO and the continuous accumulation of data, it is foreseeable that this highest-energy astronomical research that explores extreme cosmic astrophysics will show an unknown "ultra-high-energy universe" full of novel phenomena.
The third is that gamma-ray photons with an energy exceeding 1PeV first appeared in the Cygnus region and the Crab Nebula, making this area that has attracted much attention as the best candidate for the source of ultra-high energy cosmic rays, which is expected to become the unraveling of the origin of cosmic rays. The breakthrough of "Mystery".
LHAASO part of the detector array.
Photo courtesy of Institute of High Energy, Chinese Academy of Sciences
What are the core scientific goals and technological innovations?
LHAASO is a major national scientific and technological infrastructure with cosmic ray observation and research as the core. It is located in Haizi Mountain at an altitude of 4410 meters in Daocheng County. It covers an area of about 1.36 square kilometers and consists of 5195 electromagnetic particle detectors and 1188 Muzi detectors. A composite array composed of one square kilometer ground shower particle array (KM2A), 78,000 square meters of water Cherenkov detectors, and 18 wide-angle Cherenkov telescopes arranged alternately, using 4 detection technologies for omnidirectional and multivariable measurement Cosmic rays.
The core scientific goal of LHAASO is to explore the origin of high-energy cosmic rays and the related evolution of the universe, the evolution of high-energy celestial bodies, and the study of dark matter.
Extensively search for gamma-ray sources in the universe, especially the inside of the Milky Way, and accurately measure them from less than 1 TeV (1 trillion electron volts, also known as "Tai electron volts") to more than 1 PeV (1000 trillion electron volts, also known as "beats"). Electron volt") energy spectrum in a wide energy range, measuring the composition and energy spectrum of higher-energy diffuse cosmic rays, revealing the laws of cosmic rays generation, acceleration and propagation, and exploring new frontiers in physics.
In terms of technological innovation, LHAASO first has developed remote clock synchronization technology to ensure that the synchronization accuracy of each detector in the entire array can reach the sub-nanosecond level; second, with the assistance of high-speed front-end signal digitization, high-speed data transmission, and large-scale computing clusters Meet the requirements of cutting-edge technology such as multiple trigger modes in parallel; third, the first large-scale use of advanced detection technologies such as silicon phototubes, ultra-large photosensitive area microchannel plate photomultipliers, etc., greatly improve the spatial resolution of gamma-ray measurement and achieve lower Detection threshold energy.
Through continuous innovation, LHAASO enables humans to reach unprecedented levels in exploring deeper universes and higher-energy rays. It provides an important experimental platform for the development of cutting-edge scientific research on the atmosphere, environment, and space weather. It is also a high-level international A scientific base for cooperative research.
LHAASO ground shower particle array.
Photo courtesy of Institute of High Energy, Chinese Academy of Sciences
When will LHAASO be completed?
According to the popular science of the Institute of High Energy, Chinese Academy of Sciences, China's cosmic ray experimental research has so far gone through three stages of development:
In 1954, China's first alpine cosmic ray laboratory was built in Luoxue Mountain, Dongchuan, Yunnan, 3180 meters above sea level.
In 1989, the China-Japan cooperative cosmic ray experiment was launched in Yangbajing, Tibet, at an altitude of 4,300 meters, and the Sino-Italian ARGO-YBJ experiment was launched in 2000.
In 2009, at the Beijing Xiangshan Science Conference, Cao Zhen put forward a complete idea of building a large-scale composite detection array "high-altitude cosmic ray observatory" in high-altitude areas.
The LHAASO currently under construction is the third-generation mountain cosmic ray laboratory.
The high mountain experiment is a means of making full use of the atmosphere as a detection medium and observing on the ground in cosmic ray observation research. 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 observation method.
The main project of LHAASO started construction in 2017. In April 2019, 1/4 scale construction was completed and put into scientific operation. The construction and operation mode was started. In January 2020, 1/2 scale construction was completed and put into operation. In December of the same year Complete 3/4 scale and put into operation.
Chief scientist of LHAASO and researcher Cao Zhen from Institute of High Energy, Chinese Academy of Sciences introduced the research results.
Photo by China News Agency reporter Sun Zifa
Cao Zhen said that LHAASO will be completed as planned in 2021, becoming the world's leading ultra-high-energy gamma detection device. The follow-up long-term operation of LHAASO will carry out exploratory research on the origin of cosmic rays from many aspects.
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