A basket of important achievements! China's Sky Eye challenges the standard model of interstellar magnetic field

The "big pot" in Guizhou has recently produced a lot of "delicious dishes".

On January 6, Nature magazine published the latest results of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), known as the "China Sky Eye", as a cover article.

In this achievement, an international cooperation team led by Li Di, a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, used the FAST platform and the original neutral hydrogen narrow line self-absorption method to obtain for the first time high-confidence Zeeman effect measurement results in the protostellar nuclear envelope.

The study found that the interstellar medium has a coherent magnetic field structure that is different from the prediction of the standard model, providing important observational evidence for solving the "magnetic flux problem", one of the three classic problems of star formation.

The cover design of Nature magazine shows the interstellar medium and magnetic field in the Taurus molecular cloud region. The curve is the magnetic field direction map measured by the Planck satellite, and the background nebula comes from the dust image taken by the Herschel Space Telescope.

[Major achievement, challenging the standard model of interstellar magnetic field]

Magnetic fields play an important and complex role in the formation of stars, planets and life.

The "magnetic flux problem" is one of the three classic problems in star formation. Measuring the interstellar magnetic field strength of molecular clouds is a common challenge for the global astronomical community.

Stars are born in molecular clouds, where dense regions collapse and eventually form stars.

The standard model of stellar magnetic fields holds that magnetic fields and gravity are opposing forces during star formation. In areas of high molecular cloud density, the greater the gravity, the stronger the magnetic field.

According to this model, gravity and magnetic fields keep pulling so hard that it takes tens of millions of years for a star to form.

Measuring the strength of the interstellar magnetic field of a molecular cloud is not an easy task. Currently, the only method available for measuring the strength of the magnetic field is the "Zeeman effect".

In order to better measure the interstellar magnetic field, Li Di's team took a different approach and developed an original method to measure the interstellar magnetic field by measuring the spectral lines of hydrogen atoms - the neutral hydrogen narrow line self-absorption method.

Using FAST, researchers measured the magnetic field strength of the L1544 molecular cloud envelope, and for the first time achieved the detection of the Zeeman effect using the original neutral hydrogen narrow line self-absorption method. They also achieved a breakthrough from "0 to 1" in using atomic radiation to detect the magnetic field of molecular clouds.

The researchers found that, contrary to the predictions of the standard model, the interstellar medium has a basically consistent and coherent magnetic field structure from the cold neutral gas in the outer periphery of the star to the protostellar core.

"Therefore, we have reduced the time for star formation from tens of millions of years to millions of years," said Li Qi.

Picture丨TuChong Creative

[In 2021, a basket of scientific achievements]

Continued discovery of millisecond pulsars;

FAST's neutral hydrogen spectrum has made significant progress in measuring interstellar magnetic fields;

Obtained the largest sample of fast radio burst events to date;

The complete energy spectrum and double-peak structure of the fast radio burst rate are revealed for the first time

…

In 2021, scientists achieved a number of important scientific research results relying on the "China Sky Eye" FAST.

Left: Energy distribution of the average hourly burst rate of the fast radio burst FRB 121102. At 90% detection completeness at the low energy end, the burst rate began to decrease below the characteristic energy E0=4.8x1037erg, showing a complex energy distribution.

Right: An artistic imagination of FAST's observation of a fast radio burst. The pulses in the picture come from real data of FAST's observation of FRB121102.

Image copyright: National Astronomical Observatory

Left: PSR J0318+0253 position and integrated pulse profile. a) Radio-band integrated profile from one-hour FAST tracking observation; b) Gamma photon integrated pulse profile obtained by folding Fermi-LAT's 9-year accumulated data.

Right: Artistic conception of the FAST-FermiLAT collaboration conducting pulsar observations, cover of Science China issue 12, 2021.

To date, FAST has discovered about 500 pulsars, making it the most efficient device in the world for discovering pulsars since its operation.

Wang Pei, an associate researcher at the National Astronomical Observatory, introduced that the FAST multi-science target survey has discovered at least six new fast radio bursts, and is making unique contributions to revealing the mechanism of this mysterious phenomenon in the universe and advancing this new field of astronomy.

Panoramic view of the "China Sky Eye" taken on December 19, 2021 (taken during maintenance, drone photo). Photo by Xinhua News Agency reporter Ou Dongqu

【Extended Reading】

The Five-hundred-meter Aperture Spherical Radio Telescope (FAST), known as the "China Sky Eye", is a giant astronomical telescope and a national treasure. The China Sky Eye was completed and put into use on September 25, 2016, and officially opened for operation after passing the national acceptance on January 11, 2020. It is currently the world's largest and most sensitive radio telescope.

Panoramic view of the "China Sky Eye" taken on December 19, 2021 (taken during maintenance, drone photo). Photo by Xinhua News Agency reporter Ou Dongqu

Since FAST passed the national acceptance in January 2020, its operating efficiency and quality have been continuously improved, with an annual observation time of more than 5,300 hours. In March 2021, FAST was officially opened to the world for sharing, and 27 international projects from 14 countries (excluding China) have been approved and started scientific observations.

Based on its obvious advantage of ultra-high sensitivity, FAST has become a powerful tool for sky observation in the field of medium and low frequency radio astronomy, and will produce more scientific results in the future that will deepen human understanding of the universe.

Let us look forward to it together!

Comprehensive sources: Xinhua News Agency, National Astronomical Observatory of the Chinese Academy of Sciences, Science and Technology Daily, China Science Daily, etc.

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