By Lydia Amazouz Published on May 13, 2024 17:30
Collected at : https://dailygalaxy.com/2024/05/magnetic-toroids-discovered-milky-way-halo
For decades, many astronomers around the world have struggled to determine large-scale magnetic field features in the Milky Way.
In a recent study published in The Astrophysical Journal on May 10, Dr. Xu Jun and Professor Han Jinlin from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) discovered massive magnetic toroids in the Milky Way’s halo, which are critical for cosmic ray propagation and provide crucial constraints on the physical processes in the interstellar medium and the origin of cosmic magnetic fields.
What Do Magnetic Toroids in the Milky Way’s Halo Tell Us About Galactic Magnetism?
In astronomy, a magnetic toroid is a configuration of magnetic fields that takes the form of a torus or donut-shaped structure. These magnetic toroids can span tremendous distances, ranging from small-scale structures within star-forming regions to massive formations that span hundreds of light-years across galactic halos.
The production and presence of magnetic toroids are extremely important in astrophysical contexts, influencing a wide range of cosmic processes and phenomena. Within the interstellar medium (ISM), magnetic structures shape the dynamics of gas and dust clouds, influencing their fragmentation, compression, and eventual star formation. Furthermore, magnetic toroids play an important role in regulating cosmic ray propagation and supernova remnants’ energies.
Magnetic toroid observations reveal important information about the magnetic environment of galaxies, including our own Milky Way. Their identification in the Milky Way’s halo, the diffuse and tenuous region encircling the galactic disk, reveals a hitherto unknown feature of the galaxy’s magnetic construction.
Decades-Long Study Reveals Extensive Toroidal Magnetic Fields Surrounding the Milky Way
Professor Han, a top scientist in this field, has identified the magnetic field structures across the spiral arms of the galactic disk using a long-term study to measure pulsar polarization and Faraday effects.
In 1997, he discovered a striking anti-symmetry in 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’s halo have a toroidal field structure, with reversed magnetic field directions below and above the galactic plane.
For decades, astronomers have struggled to determine the size of these toroids and the strength of their magnetic fields. They assumed that the anti-symmetry of the sky distribution of Faraday effects of radio sources may be caused simply by the interstellar medium in the region of the sun, because pulsars and some adjacent radio-emission objects, which are relatively close to the sun, reveal Faraday effects that are consistent with anti-symmetry.
The goal is to demonstrate whether or not magnetic fields in the massive cosmic halo have a toroidal shape outside of the sun.
Prof. Han proposed in this study that the Faraday rotation from the interstellar medium near the sun could be counted by measuring a large number of pulsars, some of which were recently obtained by the Five-hundred Aperture Spherical Radio Telescope (FAST), and then subtracting the contribution from background cosmic source measurements.
Dr. Xu collected all Faraday rotation measurement data during the last 30 years. Scientists discovered that the anti-symmetry of Faraday rotation measurements resulting from the medium in the galactic halo exists throughout the sky, from the center to the anti-center of our Milky Way, implying that toroidal magnetic fields with such an odd symmetry have a massive size, ranging in radius from 6,000 light-years to 50,000 light-years from the Milky Way’s center.
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