Looking up at the stars, do you wonder: Where does the universe we live in come from? What exactly is in the universe? Where does the future go?
On the Tibetan Plateau, there is a group of scientists who are trying to find answers.
At 4,410 meters above sea level, in Haizi Mountain, Daocheng County, Sichuan Province, a "big net" covering an area of about 1.36 square kilometers is spread out to capture cosmic rays known as "cosmic missiles." This is the high-altitude cosmic ray observatory supported by the National Development and Reform Commission, nicknamed "Lasso" (LHAASO).
Overlooking the high-altitude cosmic ray observatory under construction. Xinhua News Agency (Courtesy of Institute of High Energy Physics, Chinese Academy of Sciences)
High-energy cosmic rays are high-energy particles from cosmic space, whose energy spans 109 to 1020 electron volts, which are mainly composed of protons and nuclei of various elements, and include a small number of electrons and photons.
Cosmic rays pervade the entire universe, carrying important scientific information such as the origin of the universe, the evolution of celestial bodies, solar activity and the earth's space environment. Studying cosmic rays and their origins is one of the most fundamental problems in modern physics and an important way for humans to explore the universe.
"The core scientific objectives of LHAASO are to explore the origin of high-energy cosmic rays and related cosmic evolution and high-energy celestial activity, and to search for dark matter; to search extensively for gamma-ray sources in the universe, especially in the interior of the Milky Way." Cao Zhen, chief scientist of LHAASO and researcher of the Institute of High Energy Physics of the Chinese Academy of Sciences, introduced that LHAASO studies cosmic rays by capturing photons, and the nodes of this "big net" are 5216 electromagnetic particle detectors and 1188 muzi detectors arranged on the ground, and the center of the "big net" is the water Cherenkov detector covering an area of 78,000 square meters, and the outside of the water Cherenkov detector is 18 wide-angle Cherenkov telescopes.
Staff build on-site hoisting telescopes at high-altitude cosmic ray observatories. Xinhua News Agency (Courtesy of Institute of High Energy Physics, Chinese Academy of Sciences)
What makes Cao Zhen proud is that LHASSO has the highest ultra-high energy gamma ray detection sensitivity, very high energy gamma ray survey sensitivity, and the widest energy coverage to accurately measure the cosmic ray energy spectrum and composition, which is not only the most advanced ground-based cosmic ray detection station in the world, but also can occupy the commanding heights of such experimental research fields for a long time.
LHAASO, which is still in trial operation, has produced world-class original results: in May 2021, the international academic journal Nature published the latest results of the LHAASO International Cooperation Group - the first discovery of a large number of ultra-high-energy cosmic ray accelerators in the Milky Way, setting a goal for the search for the source of ultra-high-energy cosmic rays. At the same time, LHAASO recorded gamma photons with an energy of 1.4 beats (beats = quadrillion) electron volts. This is the highest energy photon observed by human beings, breaking through the traditional understanding of particle acceleration in the milky way and opening the era of "ultra-high-energy gamma astronomy".
In addition to these astrophysical discoveries, LHAASO can also play a role in other fields. "For example, we work with meteorologists to explore the relationship between lightning and cosmic rays. For example, cosmic rays are affected by solar ejections when they reach the Earth, and we can also try to use cosmic ray data for space weather forecasting. In addition, LHAASO is built on the Qinghai-Tibet Plateau and also carries out aerosol measurements, and combined with this special geographical location, we have joined forces with meteorological research units to open up a new site for ecological and environmental research. Cao Zhen revealed.
Interior view of pool 1 of the high-altitude cosmic ray observatory Water Cherenkov Probe Array. Xinhua News Agency (Courtesy of Institute of High Energy Physics, Chinese Academy of Sciences)
LHAASO is China's third-generation alpine cosmic ray experimental station, from students to chief scientists, Cao Zhen has personally experienced the process of Chinese scientists in this field from following and running to leading. Cao Zhen said: "In recent years, countries have paid more and more attention to basic research, and we are confident of maintaining an international leading edge in this field. At the time of LHAASO's planning, we had already left room for upgrading, and we were exploring a new generation of cosmic ray detection equipment – now we want to capture photons, and in the future we want to capture neutrinos, and finally solve the mystery of the century of cosmic rays. ”
(Reporter Qi Fang)
Source: Guangming Daily (December 23, 2021, 01 edition)
Editor-in-charge: Wang Zimo
Editor: Xing Yanyan Zhang Yongqun