Astronomers have mapped the Milky Way’s magnetic field using a tilted 3D plane rather than a vertical wall. Published in 2026, the Dominion Radio Astrophysical Observatory survey analyzed northern sky polarization to reveal complex, dynamic structures across the galaxy.
For generations, charting the Milky Way required looking through an invisible haze. Without a magnetic field, the galaxy would collapse in on itself due to gravity, making accurate models essential for understanding how it will evolve. Yet mapping that magnetic architecture from an internal vantage point has challenged astronomers for decades, forcing researchers to infer invisible field lines from the subtle ways radio waves shift on their journey to Earth.
A new radio survey now shatters old assumptions about how those forces are arranged. An international team led by researchers at UBC Okanagan and the University of Calgary has published the sharpest map yet of the Milky Way’s magnetic field, revealing a structure far more intricate than scientists anticipated. The findings were detailed in two studies published this month in The Astrophysical Journal and The Astrophysical Journal Supplement Series.
Unlocking the Northern Sky with the DRAGONS Survey
At the center of this mapping effort is the Global Magneto-Ionic Medium Survey of the Northern Sky, known as DRAGONS. Led by former UBCO postdoctoral researcher Dr. Anna Ordog, the survey utilized a 15-metre radio telescope at the Dominion Radio Astrophysical Observatory near Penticton, British Columbia, to scan the entire northern sky across a wide span of frequencies from 350 to 1,030 megahertz.
Dr. Alex Hill, an assistant professor in the Irving K. Barber Faculty of Science at UBCO, analyzed observations alongside colleagues using broadband Faraday rotation data. The approach traces back to a theoretical concept proposed in 1966: observing polarized radio waves across multiple frequencies allows scientists to reconstruct magnetic fields in three dimensions rather than flattening them into an averaged signal. At the time, the required instruments did not exist.
“The 15m is the ideal instrument for this all-sky survey of large-scale magnetized structures—it can scan rapidly, effectively ‘painting’ a map of the polarized sky in just six months.”
The telescope itself was originally built as a prototype antenna for the SKA project under construction in Southern Africa and Western Australia. Students from UBCO and the University of Calgary tested first-light signals, developed algorithms to weed out human-made radio interference, and assessed data quality for the instrument’s maiden scientific campaign.
Tracing Faraday Rotation and Complex Fields
To read the invisible magnetic field, the research team measured a phenomenon called Faraday rotation. When linearly polarized radio waves travel through free electrons threaded by a magnetic field, their orientation rotates. The amount of rotation depends on electron density, field strength, wavelength squared, and distance along the line of sight.
Rebecca Booth, a PhD candidate working with Dr. Jo-Anne Brown at the University of Calgary, explained the process using a terrestrial analogy.
Because diffuse synchrotron radiation generates throughout the same plasma that rotates it, signals frequently become Faraday complex,
with multiple overlapping layers. The broad frequency coverage of the DRAGONS dataset allowed astronomers to use Faraday synthesis to separate those overlapping features and expose structural details that vanished in narrower, older surveys.
Dr. Tom Landecker, an astronomer emeritus at DRAO and adjunct professor, noted that more than half the sky contains complex magnetic structures rather than simple, uniform fields, calling this prevalence the team’s biggest surprise.
Redrawing the Sagittarius Arm Magnetic Reversal
The new dataset also resolved a long-standing puzzle regarding the Sagittarius Arm. Astronomers have long known that the large-scale field near the Sun points generally clockwise when viewed from the north Galactic pole, while the field farther inward toward the Sagittarius Arm points counterclockwise.
Previously, diagrams depicted that reversal as a vertical architectural wall slicing straight through the Galactic disc. Booth’s new work, published as the second of the team’s two papers, replaces that rigid barrier with an inclined plane.
“My work presents a new three-dimensional model for the magnetic field reversal. From Earth, this would appear as the diagonal that we observe in the data.”
Dr. Brown recalled the moment the discovery materialized from the numbers. Then one day, Anna brought in some data, and I went, 'O.M.G., the reversal's diagonal!'
What the New Model Means for Galactic Evolution
The diagonal model accounts for earlier clues found in rotation-measure maps, including a 2017 study by Dr. Ordog that spotted a diagonal gradient across the Sagittarius-Carina reversal. The tilted plane passes above our local region of space, with a central-plane intercept lying roughly 800 to 1,800 light-years toward the Galactic centre.
By releasing the complete dataset and the new 3D model, the research team has provided astronomers worldwide with tools to refine simulations of galactic dynamics. As researchers continue analyzing data from the northern sky survey, the physics governing the invisible forces holding the Milky Way together come into sharper, more complex focus than ever before.
