A team of researchers from McGill University and ETH Zurich has proposed a novel mechanism for the generation of cosmological magnetic fields, as detailed in a study published in Physical Review Letters on February 15, 2026. This mechanism focuses on ultralight dark matter, theorized to consist of particles with extremely low mass that interact weakly with ordinary matter.
Tiny, uniform magnetic fields are believed to permeate the universe, influencing various cosmological processes. Yet, the precise origins of these fields have long remained elusive. According to co-authors Robert Brandenberger, Jurg Frohlich, and Hao Jiao, the new research builds on ideas from previous studies conducted in 1997, 2000, and 2012, which aimed to understand the underlying physics behind these magnetic phenomena.
The researchers have explored the concept of parametric resonance, a phenomenon that leads to the exponential growth of fields linked to an oscillating source. Brandenberger noted that the interest in ultralight dark matter, specifically associated with a pseudo-scalar field called an axion, provides a compelling basis for their hypothesis. He explained that the oscillating nature of this axion field is expected to contribute to the amplification of electromagnetic fields, resulting in highly uniform magnetic fields on intergalactic scales.
Linking Dark Matter to Magnetic Fields
Brandenberger and his colleagues delve into the relationship between axion dark matter and cosmological magnetic fields. Their study aims to identify a mechanism that explains the generation of these fields without relying on uncertain physics from the very early universe. Focusing on the period known as recombination, approximately 380,000 years after the Big Bang, the authors argue that, following this phase, light and matter decoupled, allowing magnetic fields to persist for extended periods.
Utilizing an established interaction term from axion electrodynamics, the researchers demonstrate how an oscillating axion field can lead to the growth of magnetic fields that have survived to the present day. “Evidence for the existence of dark matter from various astronomical probes is compelling,” Brandenberger stated. He further noted that their assumption of dark matter being ultralight—generated by a pseudo-scalar axion field—aligns with standard cosmological theory.
The authors’ calculations indicate that the coherent oscillations of the axion field create a pseudo-tachyonic instability within the electromagnetic field, prompting rapid growth in the intensity of magnetic fields.
Reevaluating Astrophysical Theories
In comparing their findings with existing astronomical data and earlier theories, Brandenberger, Frohlich, and Jiao challenge the notion that magnetic fields on cosmological scales can only be generated during the early universe. They argue that previous assumptions about the need for new physics during cosmic inflation should be reconsidered.
While the implications of their findings are significant, the researchers acknowledge that further investigation is necessary. “We need to explore how the generated magnetic fields interact with dark matter,” Brandenberger explained. Understanding how much of the dark matter’s initial energy density converts into electromagnetic energy density remains a crucial area of study.
Additionally, the team plans to investigate the generation of magnetic fields prior to recombination when plasma effects dominate the universe’s conductivity. These aspects may require numerical simulations, potentially involving students from both institutions.
The team’s research has broader implications, particularly concerning the formation of supermassive black holes found at the centers of massive galaxies. Brandenberger highlighted a significant mystery in cosmology: the origin of numerous black hole candidates observed at high redshifts. He posited that their proposed mechanism could explain how matter collapses onto a black hole seed without fragmenting, thereby providing a pathway for further exploration.
The study offers a promising new perspective on the interplay between dark matter and the universe’s magnetic fields, paving the way for future research that could deepen our understanding of cosmic evolution.
