Beijing, May 14 (Xinhua) — The National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) announced to the media on May 14 that Dr. Xu Jun and Researcher Han Jinlin of the observatory, by analyzing the distribution data of the Faraday rotation effect of pulsars within the Milky Way and extragalactic radio sources outside it, **have found through research that there is a huge magnetic torus structure in the Galactic halo (the Milky Way halo), with the torus extending from 6,000 light-years from the Galactic Center all the way out to 50,000 light-years.

Schematic diagram of the huge magnetic torus structure in the Galactic halo. Image courtesy of the National Astronomical Observatories, Chinese Academy of Sciences.

　　This landmark study of the Milky Way's magnetic field by Chinese scientists has recently been published in the international scientific journal The Astrophysical Journal (ApJ), providing crucial observational results for research fields such as cosmic-ray particle propagation, galactic gas dynamics, and cosmic magnetic field evolution.

　　Xu Jun, **author of the paper, explained that the origin and evolution of cosmic magnetic fields is a major long-standing unsolved problem in astrophysics, and is also a priority topic for the establishment of many large radio telescope projects such as the Square Kilometre Array (SKA), all of which are developing and enhancing their polarimetric measurement capabilities in the hope of making progress in this direction.

　　Among these, measuring the large-scale magnetic field structure of the Milky Way is a rather challenging task. Researcher Han Jinlin, a pioneer in this research field, has been deeply engaged in Milky Way magnetic field research for the past 30 years. By observing the Faraday rotation effect of large numbers of pulsars and extragalactic radio sources, he measured the large-scale magnetic field structure of the Galactic disk region (the Galactic disk) and found that the direction of the large-scale magnetic field in the Galactic disk follows the spiral arms and reverses between the arms.

　　In the Galactic halo region, Han Jinlin and colleagues, as early as 1997, were the first to identify that the Faraday rotation effect exhibits an antisymmetric sign distribution in the inner Galactic sky, indicating that the Galactic halo above and below the Galactic disk has an azimuthal magnetic field structure with opposite directions. This was subsequently confirmed by more astronomical observation data and widely adopted by the international astronomical community, becoming a basic element of models of the Milky Way's magnetic field structure and being written into many classic international textbooks.

　　Han Jinlin, corresponding author of the paper, pointed out that the size and strength of the halo magnetic torus structure had been difficult to measure for more than 20 years, because pulsars and other celestial bodies in the halo region near the Sun also exhibit an antisymmetric distribution of the Faraday effect. Some international scholars speculated whether the antisymmetric Faraday sky might be dominated by the interstellar medium in a local region of the Milky Way near the Sun. "So, does this magnetic torus exist throughout the entire Galactic halo, or is it produced only in a local region? What exactly are the strength and size of the halo magnetic torus?"

　　To address these questions, Han Jinlin innovatively proposed in this study that the measured Faraday rotation measures of pulsars near the Sun be subtracted, as the contribution of the local interstellar medium, from the numerical values of the Faraday effect sky distribution of extragalactic radio sources, thereby obtaining the Faraday rotation effect distribution of the huge Galactic halo. Xu Jun collected all the relevant data and, using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), known as "China's Sky Eye," newly measured data for many faint pulsars.

　　After analyzing the data according to this innovative idea, they found that the average Faraday effect over the entire sky exhibits an antisymmetric distribution with respect to Galactic coordinates, and that the antisymmetric distribution is no longer confined to the inner Galactic region but fills the entire sky, extending from the Galactic Center region all the way to the opposite direction. The results of this study indicate that the magnetic torus in the Galactic halo extends from 6,000 light-years from the Galactic Center all the way out to 50,000 light-years (the Sun is located at about 30,000 light-years). The interstellar medium in the local region near the Sun is clearly part of the huge magnetic torus, and its basic properties and characteristics are essentially consistent with those of the large magnetic torus, but because it is deep within the Galactic disk, its effect appears stronger.

　　"I had this idea more than 20 years ago, and I have been slowly accumulating data, and finally obtained it," Han Jinlin said.