The magnetic fields in the Milky Way halo have a toroidal structure, extending in a range of radii from 6,000 light-years to 50,000 light-years from the center of the Galaxy. The Sun is approximately 30,000 light years away. Author: NAOC
Astrophysicists discovered large magnetic toroids in The Milky Wayhaloes, which affect the propagation of cosmic rays and the physics of interstellar space. Their study, based on extensive Faraday rotation data, shows that these toroids extend throughout 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 frontier of astronomy and astrophysics. It has been selected as one of the key research areas for many large world-class radio telescopes, including the Square Kilometer (SKA) currently under construction. Determining the large-scale magnetic field structures in the Milky Way has been a major challenge for many astronomers around the world for decades.
Discovery of magnetic toroids
In a new study published in The Astrophysical journal On May 10, Dr. Jun Xu and Professor Jinlin Han of the National Astronomical Observatory of the Chinese Academy of Sciences (NAOC) discovered massive magnetic toroids in the Milky Way halo, which are fundamental to the propagation of cosmic rays and provide crucial constraints on the physical processes in the interstellar medium and the origin of cosmic rays. magnetic fields.
Professor Hahn, a leading scientist in this field of research, determined the structure of the magnetic field along the spiral arms of the galactic disk as part of a long-term project to measure the polarization of pulsars and their Faraday effects. In 1997, he discovered a surprising antisymmetry of the Faraday effects of cosmic radio sources in the sky with respect to the coordinates of our Milky Way galaxy, indicating that the magnetic fields in the Milky Way halo have a toroidal field structure, with reversed directions of the magnetic field below and above the plane of the Galaxy.
Problems in measuring magnetic fields
However, determining the size of these toroids or the strength of their magnetic fields has been a challenge for astronomers for decades. They suspected that the antisymmetry in the sky distribution of Faraday effects of radio sources could only be created by the interstellar medium near the Sun, because pulsars and some nearby radio-emitting objects that are quite close to the Sun show Faraday effects consistent with antisymmetry. The main thing is to show whether the magnetic fields in the huge halo of the Galaxy had such a toroidal structure outside the vicinity of the Sun.
Innovative research methods
In this study, Professor Hahn proposed in a novel way that the Faraday rotation of the interstellar medium in the Sun’s neighborhood can be calculated using measurements of a large number of pulsars, some of which have recently been obtained by the Five Hundredth Aperture Sphere. radio telescope (FAST) independently, and then the contribution from background cosmic source measurements could be subtracted. All Faraday rotation measurement data over the past 30 years has been collected by Dr. Xu.
By analyzing the data, the scientists found that the antisymmetry in Faraday rotation measurements caused by the environment in the Galactic halo exists across the entire sky, from the center to the anticenter of our Milky Way, meaning that the toroidal magnetic fields of this strange symmetry have enormous dimensions that exist within a radius of 6,000 light years to 50,000 light years from the center of the Milky Way.
Conclusion and impact
This research greatly advanced our understanding of the physics of the Milky Way and marked a major milestone in the study of cosmic magnetic fields.
Reference: “Huge Magnetic Toroids in the Milky Way Halo” by J. Xu and J. L. Hana, May 10, 2024 Astrophysical journal.
DOI: 10.3847/1538-4357/ad3a61