Watch the sky and the sun, explore the sea of ​​stars - Thousand-Eyed Dzi Beads "stare" at the sun, moon and stars →

On September 27, the Circular Array Solar Radio Imaging Telescope (DSRT), one of the landmark equipment of the "Space Environment Ground-based Integrated Monitoring Network" (Phase II of the Meridian Project), a major national scientific and technological infrastructure led by the National Space Science Center of the Chinese Academy of Sciences, successfully passed the process test. This national heavy equipment can not only monitor the sun's "sneezes", but also successfully detect pulsars, providing high-quality independent observation data for my country's solar physics and space weather research.

It was built in Gatong Town, Daocheng County, Ganzi Prefecture, Sichuan Province, at an altitude of 3,820 meters. It consists of 313 parabolic antennas with a diameter of 6 meters. All antennas are evenly distributed on a circle with a diameter of 1,000 meters. The 100-meter-high calibration tower in the center of the ring provides a calibration benchmark for the entire observation link. It looks like a huge "Thousand-Eyed Dzi Bead", so it is nicknamed "Thousand-Eyed Dzi Bead". It covers an area of ​​about 1 square kilometer and is currently the world's largest comprehensive aperture radio telescope .

1. Monitoring the Sun’s “sneezes”

The sun can also "sneeze", and it's quite powerful! As the closest star to the Earth, the sun may seem calm, but it actually has a lot of "movements", including sunspots, flares, solar winds... When a coronal mass ejection occurs, the sun will eject a large amount of charged particles. A strong solar eruption will release the energy of 10 billion million-ton nuclear bombs, which will have a serious impact if it rushes to the Earth.

High-tech ground systems such as high-speed railways, power grids, and oil pipelines may be paralyzed or even damaged due to induced currents generated by geomagnetic disturbances. Satellites in the sky may also be damaged by catastrophic space weather.

The "Thousand-Eyed Dzi Beads" were built to monitor the sun. The circular array can not only monitor various solar explosive activities, but also monitor the process of solar storms entering the interplanetary space. This is important for understanding the mechanism of solar explosives and the laws of sun-earth propagation, and predicting the impact of solar activities on the earth .

The core mission of DSRT is to monitor the source of space weather events on Earth in real time - the sun . "These parabolic antennas are like sunflowers, always following the direction of the sun." The signals received by the 313-unit antenna of the Thousand Eyes Dzi are transmitted back to the central machine room through an 800-meter-long optical fiber, and then processed by frequency conversion, collection and other subsequent processing, so that the radio image and spectrum of the sun can be measured like a huge "radio camera".

To put it more simply, the Thousand Eyes Dzi Bead is staring at the sun . Combined with the data from other monitoring equipment, it can calculate the time when the plasma reaches the earth, thereby providing space weather warnings for the normal operation of satellites, communication facilities, power grids, etc., and ensuring the safe operation of various equipment.

To see clearly, the location is very important. The altitude here is 3,830 meters, the air is thin and the transparency is high; the latitude is low, the observable sky area is larger; surrounded by mountains, the electromagnetic interference generated by human production activities can also be effectively isolated.

Detecting pulsars

A pulsar is a rapidly rotating neutron star produced by stellar evolution and supernova explosions. It can be used for gravitational wave detection, black hole and other related research.

Simply put, a pulsar is a rotating neutron star , but not all rotating neutron stars are pulsars, because the vast majority (almost all) neutron stars rotate.

A very notable characteristic of neutron stars is that they release powerful radiation from the magnetic poles of the star. The magnetic poles do not coincide with the rotation axis of the pulsar, but are separated by a certain distance. In this way, when the neutron star rotates once, the electromagnetic radiation sweeps across the space like a lighthouse. When this radiation pulse sweeps across the earth, it is captured by the earth's radio telescope, and people discover a new pulsar.

So to be precise, a pulsar is a rotating neutron star whose magnetic energy radiation sweeps across the Earth, becoming a neutron star. Because neutron stars are very small, generally with a radius of about 10 kilometers, it is difficult to detect without this pulse radiation .

Pulsars rotate very fast. The first pulsar was discovered in 1967. The time interval between each two pulses was only 1.337 seconds, which means that this pulsar rotates once every 1.337 seconds. Of all the pulsars discovered in the world, the longest pulse interval is only 11.765735 seconds and the shortest is only 0.0014 seconds.

The pulses of a pulsar are like a human pulse or a clock, repeating over and over again with great precision and a very stable period.

DSRT has successfully acquired a series of continuous radio images and identified pulsar flashes in real time from continuous radio images for the first time. DSRT has thus started the "copy" mission of observing pulsars and fast radio bursts.

In March 2023, the Ring Array, which was in the system debugging stage, carried out China's first pulsar detection experiment based on radio image sequences, and successfully identified pulsar flashes from continuous radio images . In May, the Ring Array and the European Low Frequency Array (LOFAR) conducted a joint observation experiment and achieved cross-validation. In July, the Ring Array has the ability to continuously, stably and with high quality monitor solar activity, and the radio astronomical observation capabilities such as pulsar imaging have been initially verified, and scientific trial observations have been launched.

III. Construction Difficulties and Overcoming Difficulties

To achieve the scientific observation goals of the circular array, the 313 antennas and 626 receiving links must have very good amplitude and phase consistency .

During the construction process, the project team mastered a series of key core technologies, proposed an original circular array configuration and central calibration overall plan, and broke through key technologies such as single-channel multi-ring absolute phase calibration .

The process test showed that the circular array solar radio imaging telescope has achieved continuous and stable solar radio imaging and spectrum observation capabilities with a maximum field of view of 10 solar radii , and all technical indicators have met or exceeded the requirements of the preliminary design report.

Based on the principle of "building, debugging and operating at the same time", the 16-unit imaging experiment system has begun to acquire solar imaging data since March 2022, and has accumulated a large number of solar activity images and spectral data to date.

IV. Future Prospects

In the next stage, the Ring Array will observe solar activity during the day, provide long-term high-quality data series for solar physics and space weather research, and conduct joint observations with other monitoring equipment of the Meridian Project.

In addition, the circular array will carry out joint observations with major national scientific and technological infrastructure such as the 500-meter Aperture Spherical Radio Telescope "China Sky Eye", the "China Compound Eye" radar array, and the Sanya Incoherent Scattering Radar, and is expected to play an important role in low-frequency radio surveys, pulsars, fast radio bursts, and planetary defense monitoring and early warning .

Comprehensive sources: Guangming Daily, Science and Technology Daily, Guangming Online, People's Daily Online, Time and Space News