China News Service, Beijing, December 10th (Reporter Sun Zifa) Using the 500-meter aperture spherical radio telescope (FAST), known as the "Chinese Sky Eye", a research team led by researcher Han Jinlin of the National Astronomical Observatories of the Chinese Academy of Sciences recently completed a study, revealing that Never-before-seen high-definition detail in the interstellar medium of the Milky Way. Get a high-definition image of the gas in the Milky Way.

  In the process of searching for pulsars in the Milky Way, the scientific research team simultaneously recorded the spectral line data of the interstellar medium, revealing the delicate structure of neutral hydrogen gas in the Milky Way and the diffuse characteristics of ionized gas.

They also measured the Faraday effect of a large number of faint pulsars, which revealed magnetic signatures in far-reaching regions of the Milky Way, and identified two new remnants of supernova explosions.

  This series of important research results is of great significance to the understanding of the interstellar ecological cycle in the Milky Way. Relevant papers were published as a special topic on December 10 in China's comprehensive international journal "Science in China: Physics, Mechanics and Astronomy" (SCPMA).

The distribution map of ionized gas in the interstellar space of the Milky Way revealed by FAST (accumulation of speed range -40km/s to +120km/s).

Photo courtesy of the National Astronomical Observatory

The interstellar medium of the Milky Way hides the mysteries of life and death of stars

  Researcher Han Jinlin said that bright stars gather in the night sky to form a Milky Way across the sky.

As the home of human beings in the vast universe, there are still many mysteries about the structure and composition of the Milky Way: the vast interstellar space between hundreds of billions of stars in the Milky Way is not empty, but is filled with a thin interstellar medium, in which the diffuse hydrogen atom gas radiates A spectral line with a frequency of 1420 megahertz (MHz); dense hydrogen atoms converge and cool to form hydrogen molecular clouds, and a new generation of stars is bred in the core of high-density clouds; newborn bright stars can ionize the surrounding gas.

  Stars evolve from birth to death, some of which eventually explode as supernovae, producing supernova remnants and pulsars.

The blast shock compresses the gas in interstellar space, accelerating electrons to nearly the speed of light.

These high-speed electrons move in the interstellar magnetic field, radiating weak radio waves.

The interstellar medium of the Milky Way hides the mystery of the life and death of stars, and has always been the goal of astronomers' constant exploration.

The distribution map of the interstellar hydrogen atom gas revealed by FAST (accumulation of speed range -150km/s to +150km/s).

Photo courtesy of the National Astronomical Observatory

Design and start the Galactic Plane Pulsar Snapshot Survey

  Han Jinlin pointed out that the "China Sky Eye" is currently the most sensitive single-aperture radio telescope in the world, because it is equipped with a high-sensitivity L-band 19-beam cooling receiver, making it a powerful tool for discovering pulsars and studying the interstellar medium of the Milky Way.

The research team ingeniously designed and launched the Galactic Plane Pulsar Snapshot Survey in 2019. It has discovered more than 500 pulsars in less than 3 years, and the brightness is an order of magnitude weaker than the previously discovered pulsars.

While searching for pulsars, they simultaneously recorded the spectral line data of interstellar gas radiation, which has the characteristics of high sensitivity, high spectral resolution, and high spatial resolution. It is an extremely valuable resource for studying the structure of the Milky Way and the interstellar ecological cycle.

The team recently completed the processing of spectral line data for the first region of the Milky Way, and released the latest research results on atomic gas, ionized gas, magnetic fields, and radio radiation in the interstellar space of the Milky Way.

  In the first data release, "China Sky Eye" detected the sky distribution map of neutral hydrogen atom gas in a sky area of ​​88 square degrees between 33 degrees to 55 degrees of silver longitude and ±2 degrees of silver latitude. In progress, the preliminary results are already the most sensitive detection of hydrogen atom gas in the world so far, showing unprecedented details of the distribution of hydrogen atom gas, even 60,000 light years away from the center of the Milky Way, which cannot be seen by other telescopes The small cloud clusters in Qing Dynasty provide high-quality observation data sets for cutting-edge topics such as the study of gas dynamics and spiral arm structure of the Milky Way.

Professor Dickey from Australia commented, "Compared with all the previous surveys to detect the hydrogen atom gas in the Milky Way, the improvement in the angular resolution and sensitivity of the spectral line measurement of the Chinese Sky Eye is impressive. The publication of the first paper is a Landmark achievement".

  The ionized gas of interstellar space is the last major unexplored component of the Milky Way.

Han Jinlin's team also processed the hydrogen atom recombination lines in this Milky Way region, and obtained the distribution of ionized gas in the interstellar space, revealing the high-brightness regions ionized by bright stars and the diffuse gas of unknown origin. Ecological cycle and star formation studies provide indispensable rare datasets.

Experts from the National Astronomical Observatory of the United States said, "This is the radio composite line survey with the highest detection sensitivity so far, because it has a high enough spatial resolution to distinguish the diffuse ionized gas composition from the ionized area around the star. For diffuse gas , large telescopes like FAST can do the best detection."

The journal cover of the latest published series of special monographs.

Photo courtesy of the National Astronomical Observatory

Study confirms remnants of two supernova explosions

  In the interstellar medium of the Milky Way, the magnetic field permeates the entire galaxy, making it extremely difficult to measure and study.

Relying on the sensitivity advantage of "China Sky Eye", Han Jinlin's team newly measured the polarization and Faraday effect of 134 halo faint pulsars, and found that the magnetic field strength of the halo is about 2 microgauss.

Using newly measured data on the Faraday effect of galactic-disk pulsars, there is also evidence for reversals in the direction of the magnetic field in more distant regions of the Milky Way.

They believe that without the "Chinese Sky Eye", it will be difficult to carry out such a deep range of interstellar magnetic field detection.

  As a detection test for the characteristics of the interstellar radio continuum radiation by the "China Sky Eye", the team used FAST to scan and image the 5-degree × 7-degree sky area in the Milky Way, and confirmed two large faint radio radiation structures (G203.1+6.6 and G206.7+5.9) are shell remnants of supernova explosions, one of which is very close to the sun, only about 1400 light-years away.

So far, there are only more than 300 supernova remnants known to mankind.

  Academician Jing Yipeng, editor-in-chief of this research series, said, "High-sensitivity FAST observations have revealed unprecedented details of the Milky Way. The neutral hydrogen and ionized hydrogen databases published this time can be used to explore many features of the Milky Way's interstellar gas." , providing valuable data resources for astronomers worldwide".

  Han Jinlin concluded that as the world's top large radio telescope, the "China Sky Eye" has extremely precious observation time.

During the point-by-point survey of the Milky Way and the search for pulsars, the scientific research team collected data incidentally and obtained high-definition images of the gas in the Milky Way without using extra precious telescope time.

Currently, he is leading a scientific research team with an average age of 33, and is also the "Wang Shouguan Sky Survey Commando" awarded by the National Astronomical Observatory of the Chinese Academy of Sciences. He is still working hard to survey the Milky Way area visible to FAST, with the goal of finally completing the survey of the Milky Way's 2900 square degree area , future results can be expected.