Author: Chen Si
This article is from the magazine Knowledge is Power
The Invisible Cosmic Messenger: Cosmic Rays
What is a cosmic ray? Cosmic rays are a wall of high-energy particles that propagate at the speed of light near the vacuum induced in the atmosphere, and their main components are atomic nuclei, most of which are hydrogen nuclei, accounting for about 87%; followed by helium nuclei, accounting for about 12%; and there are also atomic nuclei of oxygen, nitrogen, iron, cobalt, nickel, carbon, lithium, barium, boron and other elements. In addition to the nucleus, there are also other microscopic particles such as electrons, photons, and neutrinos that have little interaction with matter.
Cosmic rays are a wall of high-energy particles propagating at the speed of light near a vacuum induced in the atmosphere (Image source/Svenburn University of Technology, Australia)
As the only material specimen outside the solar system, cosmic rays are an important way for human beings to explore the universe and its evolution. At the same time, cosmic rays are also extremely powerful natural high-energy elementary particle sources, which are also very important for the study of nuclear physics. For example, it was only when humans studied secondary cosmic rays that elementary particles such as positrons and mesons were first discovered. In addition, high-energy radiation lines can change or destroy the genetic genes of biological organisms, causing biological mutations. Therefore, cosmic rays have a significant impact on biological evolution and ecological balance on Earth. It can be seen that the detection and research of cosmic rays are of great significance to the fields of astronomy, physics and biology.
How to capture the Cosmic Messenger?
Since cosmic rays are so important, how do we capture them? This messenger is not something we can easily detect.
The vast majority of cosmic rays are charged particles, but there are magnetic fields everywhere in the universe, such as the Milky Way magnetic field, the solar magnetic field, and the Earth's magnetic field, and when the charged particles reach the earth after a long "journey", they will lose their original direction. Therefore, based on the direction of the cosmic rays observed on Earth, it is difficult to find its birthplace.
To the delight of humans, the study found that in the origin of cosmic rays, cosmic rays collide with local medium gases to produce neutral high-energy gamma rays. This helps a lot, because neutral particles are not affected by magnetic fields, so researchers can study the origin of cosmic rays by observing gamma rays on Earth and pushing them back in their original direction. Therefore, gamma rays through high-energy gamma rays, especially gamma rays with energy of 1014 electron volts (eV) and above, are currently very important means of finding the origin of cosmic rays.
The secret weapon that finds the origin of the cosmic ray: the Spicy Sorcerer
So, next, let's know a "secret weapon" that searches for the origin of cosmic rays - spicy sorcery. It is located in Haizi Mountain, Daocheng County, Sichuan Province, China, and covers an area of about 1.36 square kilometers.
Technically, There are four "killer skills": the electromagnetic particle detector array, the Muzi detector array, the water Cherenkov detector array, and the wide-angle Cherenkov telescope array. These four "killer skills" can measure secondary electromagnetic particles in cosmic ray air clusters; the muse content in cosmic ray air clusters; reconstruct the direction and energy of the arrival of primordial gamma rays or cosmic rays; and high-energy cosmic rays or high-energy gamma rays produced in the atmosphere through clusters of Cherenkov light or fluorescence.
Simulation of the high-altitude cosmic ray observatory project (drawing/Luo Mei)
Scientists predict that only extremely high-energy cosmic rays that bombard atomic nuclei in the Milky Way can produce a small amount of gamma rays, so from this perspective, we really "touch" the end of electromagnetic wave detection. Of course, this is also the end of our perception today. However, there is no doubt that the hot sorcerer has opened a new era of "ultra-high-energy gamma astronomy" for us!