The magnetic fields of the Milky Way’s halo have a circular structure that extends from 6,000 light-years in radius to 50,000 light-years from the galactic center. The Sun is about 30,000 light years away. Credit: NAOC
Astrophysicists have discovered large magnetic toroids Milky Way, which affect the propagation of cosmic rays and the physics of interstellar space. Their research, based on large-scale Faraday spin data, shows that these toroids extend across the galaxy, confirming the presence of significant toroidal magnetic fields.
The origin and evolution of cosmic magnetic fields has long been an unsolved question at the frontiers of astronomy and astrophysics research and has been chosen as one of the key research areas for many large world-class radio telescopes, including the Square Kilometer Array (SKA) under construction. Determining the large-scale structures of the magnetic field in the Milky Way has been a major challenge for many astronomers around the world for decades.
Detection of magnetic toroids
In a new study published It Astrophysical Journal On May 10, Dr. Jun Xu and Professor Jinlin Han of the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) discovered massive magnetic toroids in the Milky Way’s halo, which are fundamental to the propagation of cosmic rays and have important implications. Constraints on the origin of physical processes and cosmic magnetic fields in the interstellar medium.
A leading scientist in this research area, Professor Hahn has determined the magnetic field structures along the spiral arms of the Galactic disk through a long-term project to measure the polarization of pulsars and their Faraday effect. In 1997, he found an antisymmetry in the Faraday effect of cosmic radio sources in the sky with respect to the coordinates of our Milky Way galaxy, indicating that the magnetic fields of the Milky Way halo have a toroidal field structure. , in opposite magnetic field directions below and above the Galactic plane.
The challenges of measuring magnetic fields
However, it has been a difficult task for astronomers for decades to determine the size of these toroids or the strength of their magnetic fields. They suspected that the antisymmetry in the sky distribution of the Faraday effects of radio sources could only be caused by the interstellar medium near the Sun, as pulsars and some nearby radio emission objects quite close to the Sun show; Faraday effects correspond to antisymmetry. The key is to show whether the magnetic fields of the massive Galactic halo outside the Sun have a similar toroidal structure.
Innovative research methods
In this study, Prof. Hahn innovatively proposed that the Faraday spin of the interstellar medium near the Sun could be calculated from measurements of a large number of pulsars, some of which were recently obtained using the Five Hundred Aperture Sphere. radio telescope (FAST) independently, and the contribution from measurements of background cosmic sources can then be subtracted. All Faraday rotation measurement data over the past 30 years has been collected by Dr. Sue.
By analyzing the data, the scientists found that the antisymmetry in Faraday spin measurements caused by the Galactic halo environment exists across the entire sky from the center of our Milky Way to the anticenter, suggesting that toroidal magnetic fields of such strange symmetry have enormous dimensions that exist from the center of the Milky Way. 6,000 light-years in radius to 50,000 light-years away.
Conclusion and Implications
This study has significantly advanced our understanding of the physics of the Milky Way and is significant in the study of cosmic magnetic fields.
Reference. “Giant Magnetic Toroids in the Milky Way Halo” by J. Xu and JL Han, 10 May 2024. The Astrophysical Journal.
DOI: 10.3847/1538-4357/ad3a61