Tiny, highly uniform magnetic fields exist throughout the universe, influencing various cosmological processes. Despite their prevalence, the mechanisms behind the generation of these fields have remained elusive. A recent study conducted by researchers at McGill University and ETH Zurich has proposed a novel mechanism that may explain how these cosmological magnetic fields arise. Their findings were published in the journal Physical Review Letters on February 15, 2026.
The research team, comprised of co-authors Robert Brandenberger, Jurg Frohlich, and Hao Jiao, outlines a process involving a quantum field known as a pseudo-scalar field. This field may give rise to ultralight dark matter, which consists of particles with extremely low mass that interact only weakly with ordinary matter. As Brandenberger and Frohlich noted, “Evidence for the presence of tiny, very homogeneous magnetic fields in the universe extending over intergalactic scales has been gathered quite a long time ago.”
Historically, the origins of these magnetic fields have been a mystery. The researchers build on ideas from previous studies dating back to 1997, 2000, and 2012. They highlight the significance of parametric resonance phenomena, where fields experience exponential growth when coupled to oscillating sources.
Brandenberger explained that given the recent interest in ultralight dark matter, particularly from axions—hypothetical particles that could account for dark matter—it was plausible to consider that these particles might be responsible for amplifying electromagnetic fields. The authors assert that an efficient pseudo-tachyonic resonance channel exists, leading to the amplification of long-wavelength modes of electromagnetic fields. This could result in the creation of tiny, highly homogeneous magnetic fields on intergalactic scales.
Exploring the Link Between Axion Dark Matter and Magnetic Fields
The crux of the study is to identify a mechanism for generating cosmological magnetic fields without relying on speculative physics of the early universe. The authors focus on conditions post-recombination, approximately 380,000 years after the Big Bang, when the universe cooled enough for electrons and nuclei to combine into neutral atoms. This cooling period is crucial, as it is theorized that light and matter became decoupled, allowing magnetic fields to persist for extended periods.
By employing a well-known interaction term from axionelectrodynamics, the researchers demonstrate that the oscillating axion field can lead to the growth of magnetic fields that could endure until the present. “Evidence for the existence of dark matter gathered from various astronomical probes is, in our view, convincing,” Brandenberger stated, emphasizing the need to define what dark matter consists of.
The study proposes that ultralight dark matter generated by a pseudo-scalar axion field can coherently oscillate throughout the universe, influencing the formation of structures within it. This is a standard assumption within the context of their research.
The authors present calculations indicating that the coherent oscillations of the axion field could trigger a pseudo-tachyonic instability in the electromagnetic field, resulting in the rapid growth of magnetic fields.
Revisiting Astrophysical Theories
Brandenberger, Frohlich, and Jiao’s research also compares their theoretical predictions with existing astronomical observations. Prior to their work, it was deemed unlikely that magnetic fields on cosmological scales could survive until the present without being generated in the early universe. The team’s findings challenge this notion, suggesting that significant magnetic field generation could occur after recombination.
While their results are promising, the researchers acknowledge that further exploration is necessary to fully understand their mechanism. “We need to study how the magnetic fields generated according to our mechanism back-react on dark matter,” Brandenberger added. Essential aspects, such as determining the proportion of dark matter energy density converted into electromagnetic energy, require further investigation.
Additionally, the research team intends to study magnetic field generation before recombination, when plasma effects are significant. This aspect may necessitate numerical simulations and could involve collaboration with students at both McGill University and ETH Zurich.
The implications of this research extend to understanding the formation of supermassive black holes, which are among the largest black holes known, containing masses equivalent to hundreds of thousands to billions of solar masses. Brandenberger noted, “A major mystery in cosmology is the origin of the large number of black hole candidates that have been observed at high redshifts.”
The research underscores a potential connection between the generation of electromagnetic radiation after recombination and the conditions necessary for black holes to form, paving the way for new investigations into these cosmic phenomena.
The collaborative efforts of Brandenberger, Frohlich, and Jiao represent a significant step forward in unraveling the complexities of dark matter and its impact on the universe’s magnetic fields. As they continue their inquiries, the scientific community eagerly anticipates further developments in this fascinating area of research.
