Thank you TapTechNews user Feng Jianyi for the tip-off! TapTechNews reported on May 14th that Dr. Xu Jun from the National Astronomical Observatory of the Chinese Academy of Sciences and researcher Han Jinlin measured the large-scale magnetic field structure in the disk of the Milky Way by observing the Faraday rotation effect of a large number of pulsars and extragalactic radio sources. They found that the direction of the large-scale magnetic field in the Milky Way disk is along the spiral arms and flips between the arms. The official statement declared that this research result marks a new milestone in the study of the overall magnetic field of the Milky Way. This provides crucial observational results for the study of cosmic ray propagation, the dynamics of galaxy gas, and the evolution of cosmic magnetic fields. The related findings have been published in the international academic journal 'Astrophysical Journal' (DOI: 10.3847/1538-4357/ad3a61). The origin and evolution of cosmic magnetic fields have long been a major unresolved issue in astrophysics and a key priority topic for many large radio telescope projects, including the upcoming Square Kilometer Array (SKA). Major radio telescopes worldwide are developing and enhancing their polarization measurement capabilities in the hope of making progress in this direction. Measuring the large-scale magnetic field structure of the Milky Way is a highly challenging task. Researcher Han Jinlin has been exploring this research field for the past thirty years and recently made significant progress. Through observations of a large number of pulsars and extragalactic radio sources, he measured the large-scale magnetic field structure in the Milky Way disk and found that the direction of the large-scale magnetic field in the Milky Way is along the spiral arms and flips between the arms. In the halo region of the Milky Way, Han Jinlin and his team first confirmed in 1997 that the Faraday rotation effect has an anti-symmetric sign distribution in the Milky Way sky, indicating that there is a directionally opposite toroidal magnetic field structure in the halo above and below the Milky Way disk. Internationally renowned expert evaluations have found this result to be highly significant and it has been subsequently confirmed by more data, widely accepted by the international astronomical community, incorporated into various international classic textbooks written. However, the size and strength of the magnetic loop structure in the halo have been difficult to measure for over twenty years. Some scholars speculate whether the anti-symmetric Milky Way sky is dominated by the interstellar medium in the local region of the Milky Way near the Sun that produces the Faraday anti-symmetric distribution. Whether this magnetic loop exists throughout the entire halo or only in the local region and what is the strength and size of the halo magnetic loop have been long-standing questions. Han Jinlin proposed innovatively subtracting the local interstellar medium contribution from the numerically distributed Faraday rotation rate measurements of pulsars near the Sun from the Faraday effect sky distribution of extragalactic radio sources. This allows for the determination of the Faraday rotation effect distribution of the huge halo. Dr. Xu Jun collected all relevant data and with the help of China's FAST telescope measured many faint pulsars. After processing the data according to this idea, they found that the average Faraday effect of the whole sky shows an anti-symmetric distribution to the galactic coordinate and the anti-symmetric distribution is no longer limited to the inner galactic region but extends throughout the entire sky from the central region of the Milky Way galaxy to its opposite direction. The more shocking result indicates that the magnetic loop in the halo extends from 6,000 light-years away from the center of the Milky Way galaxy to 50,000 light-years away (with the Sun approximately 30,000 light-years away). It is evident that the local
interstellar medium near the Sun is also part of the massive magnetic loop, with its basic properties and characteristics being essentially the same as the large loop, but exhibiting stronger effects as it penetrates into the galactic disk.