Not long ago, the 500-meter spherical radio telescope was opened to scientists around the world
China Sky Eye: Let humans "see" farther
Panoramic view of "China Sky Eye" taken early in the morning. Xinhua News Agency
The Dawodang Depression in Pingtang County, Qiannan Buyi and Miao Autonomous Prefecture of Guizhou Province, is surrounded by mountains and green forests like the sea. The 500-meter spherical radio telescope (FAST), known as the "Chinese Sky Eye", is surrounded by mountains, like a giant eye on the earth, quietly gazing at the sky, searching for radio signals tens of billions of light-years away.
Scientists have poetically described that for more than half a century, the power of the cosmic signals received by humans is not enough to turn a page of paper. The distant signals are like the cicadas in the thunder, which cannot be distinguished without super sensitive ears. They look forward to using more powerful tools to observe information from distant galaxies.
Since the opening of operation in China in January 2020, with the help of brand-new design ideas, unique location and breaking the limit of the 100-meter project of the astronomical telescope, the "China Sky Eye" has so far discovered more than 300 pulsars and is in rapid radio bursts. Major breakthroughs have been made in the research field. On March 31 this year, this major scientific research infrastructure with my country’s independent intellectual property rights officially issued an invitation to astronomers around the world to salvage more "drift bottles" in the universe.
"Big eyes" looking at the universe
Standing on the viewing platform and looking down, the large scientific device with a diameter of 500 meters, built on the "tiankeng" in the karst area, looks like a silver "cauldron", which is erected on the surrounding 6 supporting towers with a height of more than 100 meters.
FAST chief scientist Li Dan said that the device is currently the largest and most sensitive single-aperture radio telescope in the world. Its observation capability is 10 times that of the 100-meter telescope in Bonn, Germany, and 2.25 times that of the 300-meter telescope in Arecibo, the United States. .
The large scientific device has a total of 4,500 triangular active reflective surfaces on the surface. Its design goal is to gather signals covering 30 football fields in a space the size of a small pill, otherwise it will be difficult to monitor the weak radio in the universe. signal. This "little pill" is the feed, and it is placed in the feed cabin-similar to a horn-like device that collects satellite signals, and it can be called the world's most expensive receiver.
Just like the sailor pulling the cable to control the direction of the sail, FAST changes the direction of the antenna pan by pulling the wire rope net, which is controlled by more than 2,000 small motors connected to the wire rope net. The whole process of changing direction is calibrated by the laser positioning system. The suspended feed cabin weighs 30 tons and is hoisted by six 400-meter-long steel cables with a moving range of up to 200 meters. The displacement of each part of the steel cable net and the feed cabin receiver must be controlled at the millimeter level before the large scientific devices can work normally.
When the wind is strong, people can hear the melodious "wind bells" from the entire FAST-that is the low-frequency sound produced by the vibration of its reflection unit. In the invisible underground, there are more than 100,000 optical fibers buried to provide guarantee for data transmission.
The birth of FAST can be traced back to the 1990s when astronomer Nan Rendong proposed to build China's own giant radio telescope. In 1994, the site selection work officially began. Nanren Donghe’s team used more than 300 maps and traveled over 1,000 depressions in southwest my country for 12 years. Finally, they selected Pingtang County, Guizhou Province, which has natural limestone topography, suitable size and inaccessible places. The scientific installations "settled down" here.
The construction process of the large scientific installation is arduous. Researchers and builders live in slab houses. There is no hot water, no toilets, and dirt roads outdoors. Even if the road is paved, it will be crushed by heavy trucks passing by.
On September 19, 2016, the FAST system was successfully integrated and debugged. For the first time, the debugging team used the overall system to detect the first pulsar signal previously discovered by humans, which means that the device can operate normally. Li Shan sighed, watching FAST step by step from an idea to a reality, it is really a miracle.
On August 27, 2017, the team achieved tracking and observation of a specific target for the first time, and stably obtained the radio signal of the target source. This means that the “eyeball” of FAST can be turned, and it also marks the most difficult and most difficult telescope. The functional debugging of the risk is completed.
"After that, FAST can overcome the rotation of the earth and track and observe the celestial target source. The sensitivity of the telescope is not only related to the receiving area, but also related to the tracking time. Just like the human eye, if you just glance at it, you can only look at it. Rough outline. If you want to see the details, you need to look carefully at the target. This is also the most important function of the device." said Jiang Peng, FAST chief engineer and researcher at the National Astronomical Observatory of the Chinese Academy of Sciences.
Possesses super "discovery power" in many fields
"Di-di-di", on the display, the curve representing the sound wave fluctuates rhythmically. Li said that this is the first pulsar discovered by FAST. Researchers convert the real pulse signal strength into audio and dynamic images, so that they can feel the regularity of the pulsar signal more truly.
A pulsar is a high-speed spinning neutron star with extremely high magnetic field and density. Its rotation period is accurate and stable, and the radiated electromagnetic wave can be regarded as a pulse signal like a pulse. Therefore, pulsars are compared to the "clock of the universe", and their accurate clock signals provide ideal tools for major scientific and technological applications such as gravitational wave detection and spacecraft navigation. Pulsars, as the product of supernova explosions after massive stars collapse, are also very important for studying cosmic phenomena such as supernova explosions.
On October 10, 2017, FAST announced its first astronomical discovery: a pulsar with a period of 1.9 seconds, 16,000 light-years away from the Earth. "That day was the most memorable day in my life, as if a child who had been conceived for a long time was born." Li Dan said.
In February 2018, a large scientific device detected the weakest millisecond pulsar in history. In fact, this pulsar has been "looked" many times by many astronomical telescopes on Earth but has not been "discovered", which fully proves the advantage of FAST in terms of sensitivity.
From the first discovery of a new pulsar to the announcement of the discovery of more than 100 pulsars at the end of the trial operation, to the breakthrough of 300 pulsars in one fell swoop...The number of pulsars discovered by FAST is second to none in the ranks of the global pulsar search team, becoming the pulsar discovery. Important contributor.
Fast radio bursts are the frontier field of scientific research. Their duration is only one thousandth of a second, but they can release the total energy radiated by the sun for a day or even a year. In 2017, scientists at Cornell University in the United States used the Arecibo telescope to discover the first repetitive radio burst and found the corresponding galaxy. Two years later, FAST captured this repeated rapid radio storm again, and continued to detect its active burst for more than a month, obtaining the largest collection of rapid radio storm events to date.
In January 2021, the team made new discoveries, using 2018 data to find 4 new fast radio bursts. "Assuming that the universe was born during the Big Bang, so far, it can be divided into four stages: infancy, juvenile, youth, and middle age. The four fast radio bursts discovered by FAST this time are all in the teenage years of the universe, which makes us explore The origin of the universe has gone a step further." Li Han said.
"Two darks, one black and three origins." This is a saying in the field of astrophysics to describe the scientific mission of astronomical telescopes. "Two darks" refer to dark matter and dark energy, "one black" is a black hole, and "three origins" are the origins of celestial bodies, the universe and life. Scientists said that in addition to the core scientific goal of searching for and discovering pulsars, FAST has super "discovery power" in many fields. It can verify many scientific laws, including gravitational theory, galaxy evolution, stars, planets, and even matter and life. The origin and other aspects of the company have the potential for breakthroughs. Its mission also includes the efficient exploration of extraterrestrial life and the search for answers to whether "aliens" exist。
Become a "world stage" for exploring the universe
At 0:00 on March 31, 2021, Beijing time, FAST issued an invitation to astronomers around the world to solicit applications for observations. All foreign application projects will participate in the review. The review results will be announced on July 20 this year, and the observation time will start in August.
The relevant person in charge of the National Astronomical Observatory of the Chinese Academy of Sciences said that FAST is fully open to the world, demonstrating the concept of full cooperation between China and the international scientific community. In open cooperation, China's scientific weapons will perform better, promote the output of major achievements, and contribute to the exploration and understanding of the universe for all mankind.
Li said that as early as when the project was approved, the original intention of expanding the horizons of the human universe was established and it will be open to scientists around the world. Scientists applying for the use of FAST require peer review, scoring based on project proposals, and time allocation by the time allocation committee. It is estimated that 10% of the observation time will be allocated to foreign scientists. There are no restrictions on the research field of observation applications, but projects that are of general interest to the scientific community will be given priority, such as multi-scientific target drift scan survey, neutral hydrogen galaxy survey, galaxy polarization survey, pulsar timing, fast radio burst observation, etc.
After years of construction and development, FAST has grown from scratch and has gradually grown into a "world stage" for scientists to explore the universe.
"Before the establishment of FAST, there was no large astronomical telescope in the world that could simultaneously observe the imaging of atomic hydrogen and the search of pulsars." Using a large scientific device, Li Dan and his team designed multiple scientific objectives to survey the sky at the same time, realizing it in one observation. Simultaneously conduct gas imaging, search for gas galaxies, capture pulsars and fast radio bursts. The team expects to achieve 1,000 new pulsars, 500,000 new galaxies, 10 billion neutral stars with 3D pixels, and 50 new fast radio bursts. "Simultaneous surveys of multiple scientific targets will greatly improve the efficiency of our scientific output."
"Teacher Nan Rendong once said that FAST not only represents the ambitions of scientists in the field of radio astronomy, but also an effort in China's astrophysics and astronomy science from catching up to surpassing." Li said that in the next two years, FAST will Committed to discovering the farthest pulsar known to mankind, it will participate in the detection of low-frequency gravitational waves, and gradually reveal the composition of the gas and galaxies in the universe... Around its own scientific goals, FAST's attempts have just begun. "Curiosity is the pleasure of scientists, and it is also necessary for human survival. Constantly exploring the unknown mysteries of the universe will achieve more results that we can't even imagine." (Yan Bingjie and Yu Jianbin)
