Discovery of Vast Magnetic Toroidal Structures Encircling the Milky Way’s Halo

A long-standing challenge for astronomers has been to map the large-scale magnetic field configurations within our galaxy.

In a breakthrough study published on May 10 in The Astrophysical Journal, Dr. Xu Jun and Professor Han Jinlin from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) revealed enormous magnetic toroidal structures embedded in the halo of the Milky Way. These formations play a key role in cosmic ray behavior and offer valuable insights into the physical mechanisms governing the interstellar medium and the genesis of galactic magnetic fields.

Insights into Galactic Magnetism from Toroidal Magnetic Fields in the Milky Way Halo

Magnetic toroids refer to magnetic field arrangements shaped like doughnuts or rings. They can manifest on various scales, from small regions within stellar nurseries to immense structures extending hundreds of light-years across galactic halos.

Add Cosmo Herald as a Preferred Source

These toroidal magnetic patterns are crucial in astrophysics, impacting many cosmic phenomena. Inside the interstellar medium (ISM), they influence the movement and interaction of gas and dust clouds, affecting processes such as fragmentation, compression, and star creation. Moreover, magnetic toroids regulate the journey of cosmic rays and the energy dynamics of supernova remnants.

Observations of magnetic toroids provide essential clues about the magnetic landscapes of galaxies, including our own. Their detection in the Milky Way’s halo—a sparse, extended region around the galactic disk—exposes a previously unrecognized aspect of our galaxy’s magnetic makeup.

Extensive Research Confirms Massive Toroidal Magnetic Fields Enveloping Our Galaxy

Professor Han has been a leader in exploring magnetic field structures tied to the Milky Way’s spiral arms, employing long-term studies involving pulsar polarization and Faraday rotation measurements.

Back in 1997, he identified a pronounced anti-symmetry pattern in the Faraday rotation signals from cosmic radio sources when mapped relative to the Milky Way’s coordinate system. This pointed to a toroidal magnetic field in the galactic halo, with magnetic orientations reversing above and below the galactic plane.

Despite this discovery, the scale and magnetic strength of these toroids remained uncertain for years. Some speculated that the observed anti-symmetry could originate from the local interstellar medium near the Sun, as nearby pulsars and nearby radio sources exhibited consistent Faraday rotation properties.

The central question was whether substantial toroidal fields existed throughout the halo beyond the Sun’s neighborhood.

Professor Han suggested that by quantifying the Faraday rotation caused by the nearby interstellar medium—using a vast dataset including recent pulsars observed by the Five-hundred Aperture Spherical Radio Telescope (FAST)—and subtracting this local effect from background cosmic radio measurements, the true halo magnetic structure could be revealed.

Dr. Xu gathered three decades of Faraday rotation data and demonstrated that this anti-symmetric pattern persists across the entire sky, spanning from the galactic center to its opposite direction. This confirms that the Milky Way’s halo hosts massive toroidal magnetic fields exhibiting odd symmetry, extending from roughly 6,000 to 50,000 light-years from the galaxy’s core.

• Categories:
• Astronomy ,
• News ,
• Science ,
• Space