"Wukong" sky survey is expected to unveil the mystery of dark matter

　　"Thirteenth Five-Year" Achievement Tour

　　In the past few days, when the whole country was celebrating the National Day and Mid-Autumn Festival, the "monkey" in the sky was still running on the sun-synchronous orbit, busy.

　　The "Wukong" research team of the Purple Mountain Observatory of the Chinese Academy of Sciences under 500 kilometers, under the leadership of the chief scientist Academician Chang Jin, is not idle, and is deeply analyzing cosmic rays and gamma ray data.

　　From the first frame of data transmission data received on December 20, 2015, to September 30, 2020, the "Wukong" satellite has been in orbit for 1,746 days and completed the ninth pass of the entire sky area. About 8.69 billion high-energy particles were processed.

　　"The design life of the Wukong is 3 years. The probe and the satellite platform are currently operating in good condition. The first extended life operation was officially carried out in January 2019 for a period of 2 years. Based on the excellent working status of the Wukong, it is expected to be in 2021. Life extension operation again in January 2008." One of the team leaders, researcher Fan Yizhong told a reporter from Science and Technology Daily.

　　The Monkey King’s "Crystal Rod" Will Dispel Dark Matter "Dark Clouds"

　　At 8:12 on December 17, 2015, my country used the Long March 2D carrier rocket at the Jiuquan Satellite Launch Center to successfully launch the dark matter particle detection satellite "Wukong", the first star of the Chinese scientific satellite series.

　　"This is the first time that Chinese scientists have placed their own high-resolution and high-energy space telescopes in space." Chang Jin said, "It is expected to profoundly change the human view of the universe and achieve major breakthroughs in space science."

　　The mission of "Wukong" is to find the dark matter of the universe.

Scientists speculate that more than 95% of the universe is dark matter and dark energy, of which dark matter accounts for 26.8%.

Dark matter does not emit light, emit electromagnetic waves, and does not participate in electromagnetic interactions. It cannot be directly "seen" with any optical or electromagnetic wave observation equipment.

　　The methods of human detection of dark matter are mainly divided into three categories: one is the detection by the collider, mainly the Large Hadron Collider at the European Nuclear Center; the other is the direct detection under the ground. Carry out relevant experiments; the third is indirect detection, mainly in space.

　　The "Wukong" satellite uses the third method.

Physicists believe that the collision of dark matter particles will produce high-energy particles, such as gamma rays, positive and negative electrons, positive and negative protons, and neutrinos.

Dark matter satellites can accurately detect these particles and find evidence of the existence of dark matter particles through their energy spectrum and spatial distribution.

　　At present, there are three well-known dark matter detectors in the world. "Wukong" is the space detector with the widest observation range and the best energy resolution in the world so far.

　　The satellite "Wukong" named after the American Monkey King in "Journey to the West" did not carry the golden hoop, but brought more than 300 "crystal rods."

　　The BGO energy device of the "Wukong" satellite contains 308 crisscrossed crystals, each of which is 2.5 cm square and 60 cm long, making it the longest BGO crystal in the world.

These beautiful "crystal rods" can measure the energy of incident particles to obtain clues about cosmic particles.

　　"Young and powerful" "Wukong" will continue to serve

　　Every morning and evening, "Wukong" will pass over China.

The three data receiving stations located in Miyun, Kashgar, and Sanya receive about 16G of data sent back by it every day.

The "Wukong" scientific research team is to analyze valuable scientific results from the accumulated data.

　　As early as 2017, the "Wukong" scientific research team has shown the world's first results: the accurate measurement of the electron cosmic ray energy spectrum in space.

In 2019, the team once again announced the accurate measurement results of the proton cosmic ray energy spectrum and found a new structure on the energy spectrum.

Scientists speculate that this may be a mark of a nearby cosmic ray source.

　　Scientists' judgments from the cosmic ray energy spectrum are accurate, there are two related factors: one is the amount of accumulated data, and the other is the interference of the background.

The amount of data is of course the more the better, and the background interference is as low as possible.

　　Therefore, the regular life of Academician Chang Jin is to wake up in the morning and read the summary report of the previous day's satellite data first, and then sleep after reading the analysis of the downloaded data on the day every night.

　　Currently, the "Wukong" scientific research team is carrying out helium nuclear cosmic ray energy spectrum analysis.

"We found that the helium nuclear energy spectrum also has an inflection structure similar to the proton spectrum, which provides important data for us to further understand the origin of cosmic rays in this century puzzle." Researcher Yuan Qiang of the Purple Mountain Observatory told reporters.

　　In addition, the Wukong team is also searching for dark matter signals in gamma-ray data, and is actively promoting the key technology of the next-generation dark matter particle detection satellite-the "Very Large Area Gamma-ray Space Telescope (VLAST)".

　　According to Fan Yizhong, "Wukong" has a design life of 3 years. It has been in service for nearly 2 years now, but it still looks "young and strong" and is expected to extend its working hours again.

　　Our reporter Zhang Ye