Scientists have discovered giant magnetic toroids in the Milky Way’s halo

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

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

The origin and evolution of cosmic magnetic fields is a long-standing open question at the frontier of astronomical and astrophysical research and has been selected as one of the key research areas for many major world-class radio telescopes, including the Square Kilometer Array (SKA) 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.

In a new study published in The Astrophysical Journal On May 10, they revealed Dr. Xu Jun and Professor Han Jinlin of the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) giant magnetic toroids in the Milky Way’s halo, which are crucial for the propagation of cosmic rays and provide fundamental constraints on physical processes in the interstellar medium and the origin of cosmic magnetic fields.

Prof. Han, a leading scientist in this field of research, 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 galaxy, which suggests 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.

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 distribution of Faraday effects of radio sources on the sky could only be produced by the interstellar medium near the Sun, since pulsars and some nearby radio-emitting objects that are relatively close to the Sun exhibit Faraday effects consistent with anti-symmetry.

The key is to show whether the magnetic fields in the vast galactic halo had such a toroidal structure outside the vicinity of the Sun.

In this study Prof. Han innovatively proposed that the Faraday rotation from the interstellar medium near the Sun could be calculated by measuring a large number of pulsars, some of which had recently been obtained with the Five Hundred Aperture Spherical. radio telescope (FAST) on their own, and then the contribution from background measurements of cosmic sources could be subtracted.

All Faraday rotation measurement data for the past 30 years was collected by Dr. Xu. Through data analysis, the researchers found that the antisymmetry of the Faraday rotation measurement caused by the medium in the galactic halo exists across the entire sky, from the center to the anticenter of our Milky Way, meaning that toroidal magnetic fields of such strange symmetry are enormous in size, ranging from 6,000 light-years within 50,000 light-years from the center of the Milky Way.

This study provides humans with a new understanding of the physics of our Milky Way and marks a milestone for research into cosmic magnetic fields.

More information:
J. Xu et al., Giant magnetic toroids in the Milky Way halo, The Astrophysical Journal (2024). DOI: 10.3847/1538-4357/ad3a61

Information from the diary:
Astrophysical Journal