Full Breakdown
University of Calgary Team Releases Detailed Map of Milky Way’s Magnetic Field, Revealing Diagonal Reversal in Sagittarius Arm
5/22/2026, 11:37:28 AM
Background & Scientific Context
Astronomers know the Milky Way’s magnetic field counters gravity, shaping gas dynamics, star formation, cosmic-ray paths, and dust alignment. Accurate mapping is essential for reliable galactic-evolution models.
Research Team, Telescope and Survey
Professor Brown (University of Calgary) led the study with Dr. Anna Ordog and PhD candidate Rebecca Booth; they used a radio telescope at the Dominion Radio Astrophysical Observatory (National Research Council Canada) and contributed data to the Global Magneto-Ionic Medium Survey (GMIMS) to map the Mil Way’s magnetic field.
Dataset and Faraday-Rotation Method
The telescope surveyed the northern sky across 300 MHz–1.8 GHz, measuring Faraday rotation—the twist of polarized waves by electrons and magnetic fields. This yielded three-dimensional magnetic structures and a high-quality dataset that supports two papers in *The Astrophysical Journal* and its Supplement Series.
Diagonal Magnetic Reversal in the Sagittarius Arm
Analysis reveals a magnetic reversal in the Sagittarius Arm where the galaxy’s overall clockwise field switches to counter-clockwise, creating a diagonal transition in the data. Ordog’s measurements first identified the pattern; Booth’s three-dimensional model shows the diagonal geometry, implying a large-scale shear or turbulence event that reoriented field lines.
Implications for Galactic Modeling
The refined map enhances simulations of galactic dynamics, star formation, and cosmic-ray transport, and offers a benchmark for other galaxies. It will improve long-term magnetic-field evolution predictions in galaxy-formation models.
Official Statements & Responses
Brown said mapping the field prevents collapse models. Ordog noted its broad frequency coverage resolves magnetic detail. Booth likened Faraday rotation to optical refraction, noting its probing power. The team added the dataset will let researchers test dynamo models.
Criticism & Gaps
The cause of the diagonal reversal remains unclear; southern-sky observations and lower-frequency polarization measurements are needed to assess its depth and prevalence.
Verbatim Quotes
- “Without a magnetic field, the galaxy would collapse in on itself due to gravity,” — Brown, Professor, University of Calgary
- “The broad coverage really lets you get at the details about the magnetic field structure,” — Dr. Anna Ordog, PhD, lead author
- “You can think of it like refraction. A straw in a glass of water looks bent because of how light interacts with matter,” — Rebecca Booth, PhD candidate
- “If you could look at the galaxy from above, the overall magnetic field is going clockwise,” — Brown
What’s Next
The team will extend GMIMS to lower declinations, combine space-based radio data, and refine three-dimensional reversal models, targeting a full-galaxy magnetic map within a decade. Results will be presented at the upcoming International Astronomical Union meeting.
