Tiny, uniform magnetic fields are found throughout the universe, influencing various cosmological processes. Despite their pervasive nature, the mechanisms behind the generation of these fields have remained largely elusive. Recently, researchers from McGill University and ETH Zurich proposed a novel mechanism that could explain this phenomenon, detailed in a paper published in Physical Review Letters on February 15, 2026.
The study focuses on a quantum field known as a pseudo-scalar field, which may lead to the existence of ultralight dark matter. This form of dark matter consists of particles with extremely low mass that interact very weakly with ordinary matter. Co-authors Robert Brandenberger, Jurg Frohlich, and Hao Jiao emphasize that evidence for the presence of these magnetic fields has been accumulating for years, yet their origin has remained a mystery.
Brandenberger and Frohlich highlight the significance of their work by referencing earlier studies from 1997, 2000, and 2012. They have been investigating parametric resonance phenomena, which involve exponential growth of fields linked to an oscillating source. Their latest findings suggest that ultralight dark matter, specifically a type called axion, could be responsible for amplifying electromagnetic fields across intergalactic scales.
The researchers established that the interactions between the oscillating axion field and the electromagnetic field lead to a mechanism producing highly homogeneous magnetic fields. They noted, “There is a very efficient pseudo-tachyonic resonance channel leading to the amplification of long-wavelength modes of the electromagnetic field, which will result in tiny highly homogeneous magnetic fields on inter-galactic scales.”
Linking Dark Matter and Magnetic Fields
In their research, the authors explore how axion dark matter may contribute to the generation of cosmological magnetic fields without relying on speculative theories about the early universe. They focus on cosmic events that occurred after the recombination period, approximately 380,000 years following the Big Bang, when the universe cooled enough for electrons and nuclei to form neutral atoms.
Once recombination took place, light and matter became less coupled, allowing magnetic fields to persist over extended periods. Their study employs a well-documented interaction term within axionelectrodynamics, which connects the pseudo-scalar axion field with the electromagnetic field. They demonstrated that this interaction can result in the growth of magnetic fields originating from an oscillating axion field, potentially enduring to the present day.
Brandenberger and Frohlich assert, “Evidence for the existence of dark matter gathered from various astronomical probes is, in our view, convincing. However, at this time, one does not know what dark matter is made of.” They assume that dark matter is “ultralight,” specifically produced by a pseudo-scalar axion field with a very small mass. This field, they suggest, has been oscillating coherently throughout the universe since recombination, with minor fluctuations that contribute to the formation of cosmic structures.
Investigating Astrophysical Implications
The researchers also aligned their theoretical predictions with existing astronomical observations and earlier hypotheses. They remarked that previous work deemed it unlikely for magnetic fields on cosmological scales to survive until the present day without being generated in the early universe during cosmic inflation. Their findings challenge this assumption, suggesting that magnetic fields can indeed form later in cosmic history.
Despite the promising nature of their study, Brandenberger and Frohlich acknowledge that further investigation is necessary to understand the detailed dynamics of their proposed mechanism. They plan to examine how the generated magnetic fields might interact with dark matter and the extent to which the initial energy density of dark matter is converted into electromagnetic energy density.
The authors also intend to explore the generation of magnetic fields prior to recombination, when plasma effects play a crucial role. They propose that this area may require numerical simulations, potentially involving students from McGill University and ETH Zurich.
Another intriguing aspect of this research relates to the formation of supermassive black holes, which reside at the centers of the most massive galaxies. 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.” They suggest that the mechanism presented in their study could yield a sufficient flux of Lyman-Werner photons to prevent fragmentation, thereby facilitating the collapse of matter onto black hole seeds.
The findings presented by Brandenberger, Frohlich, and Jiao represent a significant advancement in understanding the complex relationship between dark matter and cosmological magnetic fields, offering new avenues for future research in astrophysics.
