Astronomers have discovered massive magnetic toroids in the Milky Way’s halo

The magnetic fields in the Milky Way’s halo have a toroidal structure, extending within a radius of 6,000 light-years to 50,000 light-years from the galactic center. The Sun is about 30,000 light-years away from us. Credit: NAOC

Astrophysicists have discovered large magnetic toroids in… milky wayCorona, which affects the propagation of cosmic rays and the physics of interstellar space. Their research, based on extensive Faraday rotation data, reveals that these toroids extend across the galaxy, confirming the presence of large toroidal magnetic fields.

The origin and evolution of cosmic magnetic fields is a long-standing unresolved question at the frontiers of astronomy and astrophysics research, and has been chosen as one of the main research areas for several major world-class radio telescopes, including the Square Kilometer Array. SKA) is under construction. Identifying large-scale magnetic field structures in the Milky Way has been a major challenge for many of the world’s astronomers 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 Observatories of the Chinese Academy of Sciences (NAOC) revealed massive magnetic toroids in the Milky Way’s halo, which are fundamental to the propagation of cosmic rays and provide crucial constraints on physical processes in the interstellar medium and their origin. Cosmic magnetic fields.

Professor Hahn, a leading scientist in this field of research, was able to identify magnetic field structures along the spiral arms of the galactic disk through a long-term project to measure the polarization of pulsars and Faraday effects. In 1997, he found a striking anti-Faraday symmetry for cosmic radio sources in the sky with respect to the coordinates of our Milky Way Galaxy, suggesting 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 rings or the strength of their magnetic fields has been a difficult task for astronomers for decades. They suspected that the asymmetry in the sky distribution of Faraday effects of radio sources could only be produced by the interstellar medium in the vicinity of the Sun because pulsars and some radio-emitting NEOs, which are very close to the Sun, show Faraday effects consistent with the asymmetry. The key is to show whether magnetic fields in the vast galactic corona have such a toroidal structure outside the Sun’s circumference.

Innovative research methods

In this study, Professor Hahn innovatively proposed that the Faraday rotation of the interstellar medium in the vicinity of the Sun could be calculated from measurements of a fair number of pulsars, some of which were recently obtained by the Five-Hundred Aperture Spherical Radio Telescope (FAST) alone, The contribution can then be subtracted from measurements of the cosmic background of the sources. All Faraday rotation measurement data over the past 30 years has been collected by Dr. Shaw.

By analyzing the data, scientists found that the asymmetry in measurements of Faraday rotation resulting from the medium in the galactic halo is present in the entire sky, from the center to the anticenter of our Milky Way Galaxy, which means that toroidal magnetic fields such as this strange symmetry have a huge size, 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 study has greatly advanced our understanding of the physics of the Milky Way, and represents a milestone in research on cosmic magnetic fields.

Reference: “Massive Magnetic Rings in the Milky Way’s Halo” by J. Shaw and J.L. Han, May 10, 2024, Astrophysical Journal.
doi: 10.3847/1538-4357/ad3a61