China's Sky Eye has entered the stage of "producing more results" and "producing good results"

Guiyang, December 20 (Xinhua) -- The 2021 FAST Operation and Development Center's annual summary meeting was held at the China Sky Eye (FAST) Observation Base in Pingtang County, Guizhou Province on the morning of the 20th.

It is understood that scientific achievements have been made using the FAST telescope. FAST has discovered 509 pulsars, which is more than four times the total number of pulsars discovered by all other telescopes in the world.

A panoramic view of the "China Sky Eye" taken on December 19 (taken during maintenance, drone photo). Photo by Xinhua News Agency reporter Ou Dongqu

In addition, in 2021, two papers based on FAST data were published in the journal Nature, and another was selected as one of the highlights of 2021 by the American Astronomical Society.

At present, more than 120 scientific research papers have been published based on FAST data, with more than 590 citations. In the next stage, the FAST Operation and Development Center will accelerate the construction of the National Key Laboratory of Radio Astronomy and Technology.

A panoramic view of the "China Sky Eye" taken on December 19 (taken during maintenance, drone photo). Photo by Xinhua News Agency reporter Ou Dongqu

Chang Jin, an academician of the Chinese Academy of Sciences and director of the National Astronomical Observatory, said, "In terms of pulsar searches, FAST has discovered more than 500 pulsars in more than two years. The FAST operation team will operate FAST more efficiently, keep FAST in a high-level operating state, conduct in-depth research on neutral hydrogen surveys, including fast radio bursts, and strive to make major breakthroughs in these cutting-edge scientific fields."

A panoramic view of the "China Sky Eye" taken on December 19 (taken during maintenance, drone photo). Photo by Xinhua News Agency reporter Ou Dongqu

According to Dazhong Daily, the aperture of the "China Sky Eye" is 500 meters, and the launch area is equivalent to 30 standard football fields. If you fill it with mineral water, the 7 billion people in the world can share 4 bottles on average. How far can it see? It can see through an area of ​​more than 13 billion light years, close to the edge of the universe. At present, the "China Sky Eye" is the world's largest and most sensitive single-aperture radio telescope.

Using the principle of parabolic antenna to listen to signals from the universe from Earth

The scientific name of the "China Sky Eye" is the 500-meter Aperture Radio Telescope. Unlike common optical telescopes that observe through visible light, radio telescopes "observe" the universe by receiving invisible radio waves in the universe. There are two "windows" in the thick atmosphere above us: one is the visible light window, through which humans have observed the universe for thousands of years; the other is the radio window. In the 1930s, Karl Jansky, a pioneer in radio astronomy, accidentally discovered a signal from the center of the Milky Way, which opened the curtain of radio astronomy and promoted human understanding of the origin of the universe and the origin of life.

The "China Sky Eye" is a "powerful tool" in today's radio astronomy. What is its basic principle? We all know that parallel electromagnetic waves will converge to the focal point after encountering a parabola. For a radio telescope, the reflecting surface is made into a parabola shape, and then a receiver is placed at the focal point, so that the electromagnetic wave signals emitted by the celestial body can be collected, so as to conduct astronomical observations. The larger the area of ​​the parabola, the more signals are collected, and the more faint and distant celestial bodies can be detected. Therefore, since Karl Jansky accidentally discovered the radio astronomy observation window, astronomers from various countries have been committed to building giant radio telescopes with as large a reflecting surface as possible.

At the same time, with the large-scale use of radio by humans, more and more radio waves are generated, which interfere with the reception of space signals by humans. At the 1993 International Radio Conference, several countries, including China, proposed to build a super-large radio telescope before the earth's electromagnetic wave environment is destroyed. The following year, Chinese scientists represented by Mr. Nan Rendong began the exploration of the "China Sky Eye", opening the journey of "making the impossible possible".

With great difficulty and many breakthroughs, the "China Sky Eye" occupies a commanding position in terms of sensitivity

The size of the telescope that can be built depends on the size of the depression that can be found. It is very difficult to find a suitable depression because it must meet four conditions at the same time. First, it must be large enough and round enough, otherwise the excavation and support costs alone will make this project impossible to achieve; second, it must be far away from densely populated areas to ensure a good radio wave environment; third, it must not accumulate water, otherwise the life of the equipment will be difficult to guarantee; finally, it must have excellent geological conditions, otherwise it is impossible to build a large, high-precision astronomical observation equipment.

From 1994 to 2006, Nan Rendong led a team to select more than 300 depressions from more than 8,000 maps, and then further narrowed the scope to dozens of them. The team traveled almost all of these depressions, conducted on-site surveys, and slept in the open air. Finally, the site was determined to be the Dawodang depression in Kedu Town, Pingtang County, Guizhou.

After the site is determined, there is no ready-made experience to draw on for how to design, implement, debug and use it after construction: there is no precedent for key technologies and key materials need to be developed from scratch.

The design of the "China Sky Eye" is different from the existing single-aperture radio telescopes in the world. This is first reflected in the design of the "retina" and "pupil". The "retina" refers to the reflective surface; the "pupil" refers to the feed cabin, which is the cabin where the device system for receiving signals from outside the universe is placed.

As a world first, the "retina" of the "China Sky Eye" is an active reflective surface that can change shape, sometimes spherical and sometimes parabolic. Specifically, this huge movable "retina" is a cable net made of 6,670 steel cables, hanging on a 500-meter diameter ring beam supported by 50 huge steel columns; the cable net is covered with 4,450 pieces of more than 380 reflective surface units; under the cable net are 2,225 pull-down cables, each of which is fixed to an actuator on the ground. By manipulating the actuator and pulling the pull-down cables, the shape of the cable net can be changed, thereby collecting and observing astronomical signals.

The "pupil" of the "China Sky Eye", or the feed cabin, is also a bold breakthrough design. The "pupil" position of most traditional radio telescopes is fixed or can only be slightly adjusted. The "China Sky Eye" is completely different. It uses a new lightweight cable-driven control system, which allows the "pupil" of the "China Sky Eye" to freely change its angle and position, and more effectively collect, track and monitor more abundant cosmic electromagnetic waves.

In terms of volume, the feed cabin of the world's largest radio telescope weighed more than 1,000 tons, while the feed cabin of the "China Sky Eye" weighs only about 30 tons. The small size brings many advantages, such as effectively reducing light path obstruction and interference signals, making the beam very clean and more conducive to astronomical observation.

The breakthrough innovation in the design of the "China Sky Eye" has brought huge challenges to the manufacturing process "from drawings to reality". The process of coping with challenges is also the process of domestic precision manufacturing constantly creating miracles. For example, to achieve the world's first design of a reflective surface (i.e., cable net) that can change its shape, the steel cables that make up the cable net must have a certain degree of elasticity like a spring, and the fatigue strength is more than twice the existing standard, which is unprecedented internationally; it is also required that the processing accuracy of each steel cable must reach 1 mm, which has raised the traditional standard by an order of magnitude.

Over the past two years, scientists have continued to improve the cable body technology in all aspects, and one steel cable has to undergo 2 million fatigue tests. After nearly 100 failures, they finally successfully solved this key problem and achieved three world firsts: ultra-large span, ultra-high precision, and active displacement cable net structure.

After the construction was completed, the "China Sky Eye" entered the debugging stage. The debugging of giant telescopes involves many disciplines such as astronomy, measurement, control, electronics, mechanics, and structure. It is a highly interdisciplinary applied research. The debugging cycle of traditional large radio telescopes in the world is rarely less than 4 years. The "China Sky Eye" has created a new model, and its debugging work is also more challenging.

So far, tracking, drifting, motion scanning, weaving scanning, etc. have been realized, and functional debugging has been completed ahead of schedule. In terms of performance debugging, the "China Sky Eye" has a diameter of 500 meters, but it has to achieve millimeter-level accuracy, which is quite difficult. At present, the accuracy of the telescope measurement benchmark network has been improved to within 1 mm. Among them, the sensitivity level is 2.5 times that of the world's second largest telescope. This is the first time that a telescope built in China has occupied the commanding heights in terms of sensitivity. In addition, 19 beams have been installed, which is also of great significance: the field of view of the telescope can be expanded to 19 times the original, greatly improving the telescope's sky survey efficiency.

The patented technology of "China's Sky Eye" has been applied in many fields and continues to incubate new scientific achievements.

The "China Sky Eye" team dared to think and act. The difficulty and challenge were great. The design and construction process was not only a process of overcoming difficulties, but also a process of producing innovative results. Many patented technologies with independent intellectual property rights in my country have been born and applied. For example, ultra-high fatigue performance cable structures have been used in large sports venues, and high-precision cable structure production systems have been used in the construction of the Hong Kong-Zhuhai-Macao Bridge.

Many national and provincial construction methods were developed during the entire manufacturing and installation process. For example, in the process of laying the "retina" for the "China Sky Eye", 4,450 reflective units, 6,670 steel cables, and tens of thousands of joint bearings were assembled piece by piece, one by one, and one by one by workers at a height of dozens of meters, with zero error tolerance. These complex construction methods will help the precise construction of large and complex projects in the future.

It can be said that the "China Sky Eye" is a modern engineering miracle. It condenses the efforts of more than 20 scientific research institutions, hundreds of scientific researchers, and gathers the sweat of thousands of front-line workers. The construction conditions are difficult. Many people will have red bumps on their bodies after working on site for a few days. The damp and cold shed has no air conditioning or heating, and everyone's quilt is so damp that water is about to be squeezed out. It is often said that only China can build the "Sky Eye". I think that the "Sky Eye" relies on this spirit of never giving up and unity.

In October 2017, the first batch of scientific results of the "China Sky Eye" were made public. Today, more than 70 high-level papers have been published based on the data of the "China Sky Eye"; the number of pulsars discovered has exceeded 300, which is three times the total number discovered by all other telescopes in the world during the same period. Why is the discovery of pulsars so important? Pulsars are rapidly rotating neutron stars with extremely high density, weighing hundreds of millions of tons per cubic centimeter. It scatters light like a lighthouse, scanning the universe at all times; it rotates very fast and has a precise rotation period, and can be called the most accurate clock in the universe. Therefore, grasping pulsars is conducive to the establishment of a "cosmic navigation system" and will help humans realize the dream of interstellar travel in the future.

Next, the "China Sky Eye" will further explore frontier areas such as low-frequency gravitational wave detection, the origin of fast radio bursts, and interstellar molecules, strengthen open sharing at home and abroad, promote the output of major results, and bravely climb the world's technological peak. Our young generation of scientists will also strive to "use" the "Sky Eye" that condenses the efforts of four generations of Chinese scientists, produce more scientific research results, and promote human exploration and cognition of the universe.

Source: Xinhua News Agency Dazhong Daily