Magnetic fields in the Milky Way’s halo have a toroidal structure and extend in the radius range of 6,000 light-years to 50,000 light-years from the center of the galaxy. The sun is about 30,000 light years away. Photo credit: NAOC
Astrophysicists have discovered large magnetic toroids in it Milky Ways halo, which have implications for the propagation of cosmic rays and the physics of interstellar space. Their research, based on extensive Faraday rotation data, shows that these toroids extend across the entire galaxy, confirming the presence of significant toroidal magnetic fields.
A long-unsolved question at the frontier of astronomy and astrophysics research is the origin and development of cosmic magnetic fields. It has been selected as one of the key research areas for many large, world-class radio telescopes, including the Square Kilometer Array (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 10th, Dr. Jun Restriction of physical processes in the interstellar medium and the formation of cosmic magnetic fields.
Prof. Han, a leading scientist in this field, has determined the magnetic field structures along the spiral arms of the galactic disk through a long-term project measuring the polarization of pulsars and their Faraday effects. In 1997, he found a striking antisymmetry of the Faraday effects of cosmic radio sources in the sky with respect to the coordinates of our Milky Way, stating that the magnetic fields in the Milky Way’s halo have a toroidal field structure, with reversed magnetic field directions below and above the galactic plane.
Challenges in measuring magnetic fields
However, determining the size of these toroids or the strength of their magnetic fields has been a difficult task for astronomers for decades. They suspected that the antisymmetry of the sky distribution of Faraday effects of radio sources could be generated solely by the interstellar medium near the Sun, since pulsars and some nearby radio emission objects located quite close to the Sun are visible Faraday effects in Harmony with antisymmetry. The key is to show whether or not the magnetic fields in the giant galactic halo outside the Sun’s vicinity had such a toroidal structure.
Innovative research methods
In this study, Prof. Han innovatively proposed that Faraday rotation from the interstellar medium near the Sun could be counted through measurements of a large number of pulsars, some of which were recently detected using the Five-hundred Aperture Spherical radio telescope (FAST) itself, and then the contribution could be subtracted from the measurements of the cosmic background sources. All Faraday rotation measurement data for the last 30 years were compiled by Dr. Xu collected.
Through data analysis, scientists found that the antisymmetry of Faraday rotation measurements caused by the medium in the galactic halo exists throughout the sky, from the center to the anticenter of our Milky Way, suggesting that toroidal magnetic fields exist With such a strange Due to their symmetry, they are enormous in size and exist within a radius range of 6,000 light-years to 50,000 light-years from the center of the Milky Way.
Conclusion and effect
This study has significantly expanded our understanding of the physics of the Milky Way and marks a milestone in the study of cosmic magnetic fields.
Reference: “The Huge Magnetic Toroids in the Milky Way Halo” by J. Xu and JL Han, May 10, 2024, The Astrophysical Journal.
DOI: 10.3847/1538-4357/ad3a61