Chinese researchers discover ginormous magnetic toroids in halo of Milky Way galaxy

Illustration of the magnetic toroids in the halo of the Milky Way, using the Sombrero Galaxy. (Image Credit: NAOC).

New Delhi: One of the most pressing unsolved questions in astronomy is the origin and evolution of cosmic magnetic fields. Astronomers have been struggling to understand the large-scale magnetic field structures in the Milky Way for Decades. Now, scientists from China have revealed massive magnetic toroids in the halo of the Milky Way. These toroids are fundamental for the propogation of cosmic rays, and constrain the physical processes in the interstellar medium.

The scientists were able to unravel the massive structures through a long-term campaign of measuring the polariosation of pulsars and their Farady effects. The construction of the Five-hundred Aperture Spherical radio Telescope (FAST), the largest filled-dish radio telescope in the world allowed for the measurements of additional pulsars. Measurements over a period of 30 years have been used for the study.

The paper provides humans with a novel understanding of the physics of the Milky Way, and is a landmark in the understanding of cosmic magnetic fields. The researchers had earlier discovered a striking anti-symmetry of the Faraday effects of radio sources in the sky, with respect to the coordinates of our Milky Way galaxy. The magnetic field directions of the toroidal structures have been found to be reversed above and below the plane of the galaxy. A paper describing the research has been published in The Astrophysical Journal.

The Faraday Sky

The Faraday sky refers to a map of the Faraday rotation effect caused by magnetic fields of the Milky Way. As the polarised radio waves from distant sources pass through the interstellar medium, their orientation gets twisted because of magnetic fields along the line of sight. The resulting Faraday rotation provides valuable information on the distribution and strength of cosmic magnetic fields.

Scientists from around the world have assembled extensive catalogues of Faraday rotation data from compact extragalactic polarised radio sources. The data allows for the creation of sky maps with cosmic magnetic fields. However, this is painstaking work that requires decades of observations, with the map resolving to a better clarity as and when new observations are conducted.

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