The result is , The national major science and technology infrastructure in Daocheng, Sichuan “ High altitude Cosmic Ray Observatory （LHAASO）” A large number of super high energy cosmic accelerators have been found in the galaxy , And record the highest 1.4 Beat electron volt gamma photon （ pat = One quadrillion ）. This is the highest energy photon ever observed by humans , Changed our traditional understanding of galactic particle acceleration , Turn on “ Super high energy gamma literature ” Era .
Is it right? “ It sounds super powerful ”, Species “ I know every word , But together, I don't know what I'm talking about ” The feeling of ？ that , Please feel it slowly ——
【 What is cosmic ray ？】
First you need to figure out what cosmic rays are .
In the universe , Countless mysterious particles are flying close to the speed of light , These mysterious particles are cosmic rays —— High energy charged particles in interstellar space . It's on 1912 Austrian physicist victor · Hess found , The latter is also honored with 1936 The Nobel Prize in physics .
In the interstellar space of the galaxy , Cosmic rays contribute 1/3 The energy density of , It's an important part of interstellar space , It also dominates astrophysical processes such as interstellar chemistry and star formation . therefore , The study of cosmic rays is of great significance for human beings to understand the universe .
The spectrum of cosmic rays is beating electron volts （1 pat =1 One quadrillion ） There is a zigzag structure nearby , This suggests that there are objects in the galaxy that can at least accelerate protons to electron beats . For the present human civilization , The beat electron volt is an energy that is hard to reach , The largest man-made particle accelerator on earth right now （ It's CERN LHC） The limit energy for accelerating particles is just 0.01 Beat electron volts or so .
The origin of these cosmic rays is equivalent to a natural particle physics laboratory , Finding these celestial bodies and studying their properties is not only an important milestone in human understanding of the universe , It may also be a key step to break through the current framework of basic physics .
【 The mystery of the century ？】
The origin of high energy cosmic rays , It's a century old mystery , There are two main difficulties ：
First of all , There are magnetic fields all over the universe , When charged particles move in a magnetic field, they will be deflected by the magnetic field . The cosmic ray has lost the position information of the source in the process of transmission from the source to the earth , Scientists can't directly locate the source by the direction of arrival of cosmic ray particles .
second , The conditions for accelerating a particle to beat electron volts are quite harsh , Even if the celestial body has a strong ability to accelerate , Only a very small number of particles can achieve such a high energy , So the signal of the ultra-high energy photons is also very weak .
In view of this situation , Instead, scientists are targeting photons produced by these cosmic rays interacting with the interstellar medium . Because the motion of photons is not affected by magnetic fields , Detected energy in 0.1 Beat photons above electron volts （ Also known as ultrahigh energy photons ） So we can locate the petv accelerator . However, before that, the mainstream detectors in the world mainly worked in 0.1 Below the electron volt energy , It's difficult to confirm the beat electron volt cosmic ray accelerator .
【 What is super high energy gamma ？】
Ultrahigh energy （UHE：>1014 Electronic volt ） Gamma astronomy is the last observation of the universe 、 It's also the highest energy electromagnetic radiation window , Because of the small number of super high energy gamma rays, they are submerged in the huge cosmic ray background , The detection of ultra-high energy gamma rays has always been a great challenge for human beings , Become virgin land that has not been reclaimed .
Super high energy gamma rays come from particles with higher energy than it does , So it can be used to trace the origin of these energetic particles 、 Acceleration and communication mechanism , That is, it can be used to discover and study cosmic high-energy particle accelerators , It's about cracking the origin of high energy cosmic rays “ The mystery of the century ” The golden key to success .
However, it is very difficult to detect ultra-high energy gamma rays , An ultra-high energy gamma ray detector must have the following five conditions at the same time ：
A large area ： Ultra high energy gamma rays are very rare , Only one or two can be received every day in an area of one square kilometer , To capture them, they need to be laid over an area of at least one square kilometer “ nets above and snares below ”;
Powerful gamma / Background discrimination can force ： These rare gamma events are mixed in the cosmic ray background thousands of times , The detector needs to have a bright eye , Accurate identification of gamma events and cosmic ray background events , To accurately pick out rare gamma ray events from thousands of backgrounds like a needle in a haystack ;
High altitude ： It takes altitude to detect ultra-high energy gamma rays 4000-5000 The snow covered plateau with a height of 200 meters , The air is thin here , Difficulty in breathing , It is the best place to detect ultra-high energy gamma rays ;
Big field of view ： A pair of eyes can only see part of the sky , There must be ten million pairs of eyes on the whole sky , Don't lose a precious example ;
all-weather ： These eyes can't blink , I want to sleep day and night , To capture all the cases ;
【 What is? LHAASO？】
China's high altitude cosmic ray observation station （LHAASO）, It is a national major science and technology infrastructure with cosmic ray observation and research as the core , It is located in Daocheng County, Sichuan Province 4410 Haizi mountain of rice , Covering an area of about 1.36 Square kilometers . It is the most sensitive ultra-high energy gamma ray detector in the world .
High altitude Cosmic Ray Observatory （LHAASO,2020/11）
Its working energy extends from TEV to petv （1 pat =1000 too ）, It not only has a huge effective detection area of one square kilometer , It is equipped with 1188 A muon detector can also accurately pick out a photon signal mixed in 100000 background events . With strong performance ,LHAASO Just rely on it 1/2 Scale stage operation 11 Data collected in the last two months , It was discovered in the Milky way 12 A super high energy gamma ray source ！
Here 12 Among the sources , It includes the Crab Nebula 、 Cygnus, star forming region and other famous objects in the field of gamma ray astronomy , There are also new sources that have never been found before . The most surprising thing is , The highest photon energy of the first two is 1 Beat electron volts , It has greatly set a new record for the highest energy of photons detected by human beings . Interestingly , The highest energy photon ever observed by humans comes from the famous constellation Cygnus “ cocoon crust ”（Cocoon）, Scientists have long believed that it is a super high energy cosmic ray source , But no hard evidence has been found .
Let's see LHAASO Cosmic ray observatory detectors
How does it work
This landmark new discovery opens a new window for the astronomical observation of ultra-high energy gamma rays , It gives us a glimpse of the turbulent undercurrent in our galaxy .LHAASO Today's scientific discoveries are just the tip of the iceberg in super high energy gamma astronomy , Its full array is expected in 2021 Completed and put into scientific operation in . We have reason to believe that , In the next few years , When the whole LHAASO After putting into use ,LHAASO With its sensitivity far beyond the current level, we will focus on the origin of high-energy cosmic rays “ The mystery of the century ” Launch an impact , Further refresh the traditional human cognition of the galaxy .
Chief editor of Red Star News Huang Haiying
Integrated voice of the Chinese Academy of Sciences 、 Science complex
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