SPACE/COSMOS
Mapping the magnetic field of the Milky Way
Two new studies reveal structural complexity in the galaxy
University of Calgary
For centuries, astronomers have been observing celestial bodies and trying to understand the mysteries of the night sky. Dr. Jo-Anne Brown, PhD, wants to map an invisible force of the Milky Way galaxy: its magnetic field.
“Without a magnetic field, the galaxy would collapse in on itself due to gravity,” says Brown, a professor in the Department of Physics and Astronomy at the University of Calgary.
“We need to know what the magnetic field of the galaxy looks like now, so we can create accurate models that predict how it will evolve.”
This month, Brown and a team of researchers have published two papers in The Astrophysical Journal and The Astrophysical Journal Supplement Series. Their discoveries include a complete dataset, which will be used by astronomers globally, and a new model that will inform theories for how the magnetic field of the Milky Way evolved.
The group used a new telescope at the Dominion Radio Astrophysical Observatory in B.C., a National Research Council Canada facility, to map the northern sky across different radio frequencies.
“The broad coverage really lets you get at the details about the magnetic field structure,” says Dr. Anna Ordog, PhD, and lead author of the first of the two studies.
The result is a comprehensive, high-quality dataset, captured as part of the Global Magneto-Ionic Medium Survey (GMIMS) project that maps the magnetic field of the Milky Way galaxy.
The data that was collected involved tracking an effect known as Faraday rotation.
“You can think of it like refraction. A straw in a glass of water looks bent because of how light interacts with matter,” says Rebecca Booth, a PhD candidate working with Brown and lead author of the second study. “Faraday rotation is a similar concept, but it’s electrons and magnetic fields in space interacting with radio waves.”
Booth’s work in the second study looked at a unique feature in the Milky Way galaxy — the Sagittarius Arm, which has a reversed magnetic field.
“If you could look at the galaxy from above, the overall magnetic field is going clockwise,” says Brown. “But, in the Sagittarius Arm, it’s going counterclockwise. We didn’t understand how the transition occurred. Then one day, Anna brought in some data, and I went, 'O.M.G., the reversal's diagonal!'"
Booth followed up on Ordog's discovery using the dataset.
“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,” Booth explains.
Journal
The Astrophysical Journal
Method of Research
Survey
Subject of Research
Not applicable
Article Title
A Three-dimensional Model for the Reversal in the Local Large-scale Interstellar Magnetic Field
Article Publication Date
29-Jan-2026
First radio signals from rare supernova reveal star’s final years
Astronomers have captured the first radio waves ever detected from a rare class of exploding star, a discovery that has given them an unprecedented look into the final years of a massive star before its death in a powerful stellar explosion called a supernova.
Their findings, published in The Astrophysical Journal Letters, focus on a stellar explosion called a Type Ibn supernova. These explosions occur when a massive star blasts apart into clouds of helium-rich gas it shed shortly before death.
Using the National Science Foundation’s Very Large Array radio telescope in New Mexico, the researchers tracked faint radio signals from the explosion over roughly 18 months. The radio waves revealed tell-tale signs of gas the star ejected just years before it blew apart — information that cannot be captured with optical telescopes alone.
Raphael Baer-Way, a third-year Ph.D. student in astronomy at the University of Virginia and lead author of the study said, “We were able to use radio observations to ‘view’ the final decade of the star’s life before the explosion. It’s like a time machine into those last important years, especially the final five when the star was losing mass intensely.”
He explained that stars giving rise to Supernovae in other galaxies are usually too dim and far away to observe directly until they explode, but if a star sheds a lot of mass before its demise, that gas can act as a “mirror” that reveals the star’s final stages when the explosion’s shockwave crashes into it. This interaction creates strong radio waves.
Baer-Way said his team found evidence that the star was likely in a binary system — two stars orbiting each other — and that interaction with a companion may have driven the dramatic mass loss immediately before the explosion.
“To lose the kind of mass we saw in just the last few years… it almost certainly requires two stars gravitationally bound to each other,” he explained.
The new radio data not only confirm that this kind of pre-explosion mass shedding happens but also open a new way to study stellar death across the universe. Until now, researchers depended mostly on optical light to infer such behavior. Radio observations add a powerful new tool to the resources available to the scientists who study these phenomena.
According to Baer-Way, the next steps are to extend this work by studying a larger sample of supernovae to see how often these intense mass-loss episodes occur and what they reveal about how stars evolve.
“Raphael’s paper has opened a new window to the Universe for studying these rare, but crucial Supernovae, by revealing that we must point our radio telescopes much earlier than previously assumed to capture their fleeting radio signals,” said Maryam Modjaz, professor of astronomy at UVA and an expert on massive star death and supernovae.
Journal
The Astrophysical Journal Letters
Article Title
The First Radio View of a Type Ibn Supernova in SN 2023fyq: Understanding the Mass-loss History in the Last Decade before the Explosion
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