Research from McGill University and ETH Zurich has introduced a new mechanism that may explain the origins of cosmological magnetic fields. Published on February 15, 2026, in the journal Physical Review Letters, the study proposes a connection between ultralight dark matter and the generation of these fields, a topic that has puzzled scientists for decades.
Tiny, uniform magnetic fields permeate the universe and influence various cosmological processes. Despite their significance, the physical mechanisms responsible for producing these fields remain largely unclear. The team, led by researchers including Robert Brandenberger and Jurg Frohlich, explored the potential of a quantum field known as a pseudo-scalar axion, which could be responsible for the existence of ultralight dark matter.
According to Brandenberger and Frohlich, “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. For a long time, the origin of these fields has remained a mystery.” Their recent work builds on earlier theories proposed in 1997, 2000, and 2012, adding depth to the ongoing exploration of dark matter and its properties.
The researchers focused on a process called parametric resonance, which leads to the exponential growth of fields attached to an oscillating source. This concept, originally identified in classical mechanics, is now being applied to current theories of dark matter. The team suggests that if ultralight dark matter oscillates coherently throughout space and interacts with the electromagnetic field, it could serve as a source for the growth of magnetic fields.
Their study demonstrates how this pseudo-scalar axion field can couple to electromagnetic fields, resulting in the amplification of long-wavelength electromagnetic modes. This amplification could explain the existence of the observed magnetic fields across vast intergalactic distances.
Connecting Axion Dark Matter to Magnetic Field Generation
Brandenberger, Frohlich, and their colleague Hao Jiao seek to establish a direct link between axion dark matter and cosmological magnetic fields. They aim to elucidate a mechanism that generates these fields without relying on speculative theories concerning early-universe physics. Their analysis focuses on the period after recombination, approximately 380,000 years following the Big Bang, when the universe cooled sufficiently for electrons and nuclei to form neutral atoms.
The researchers utilize an interaction term from axionelectrodynamics, which connects the pseudo-scalar axion field to the electromagnetic field. They postulate that this interaction could result in the sustained growth of magnetic fields generated from oscillating axion fields, persisting until the present day.
Brandenberger articulates, “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.” Their work assumes that dark matter is ultralight, generated by a pseudo-scalar axion field with an extremely low mass, which has been coherently oscillating throughout the cosmos since the time of recombination.
Implications for Astrophysical Theories
The findings challenge previously held assumptions that magnetic fields on cosmological scales could not be generated after recombination. Earlier studies had suggested that new physics pertaining to the very early universe was necessary to explain these magnetic fields. The current mechanism raises questions regarding this notion and opens new avenues for research.
Despite the promising nature of their results, Brandenberger and Frohlich note that further investigation is required to fully understand the implications of their findings. They intend to explore how the magnetic fields produced by their mechanism might interact with dark matter, including what fraction of dark matter’s initial energy density is converted into electromagnetic energy density.
The researchers emphasize the importance of studying magnetic field generation prior to recombination, when plasma effects dominate the universe’s conductivity. They anticipate that numerical simulations could provide deeper insights into this mechanism, potentially involving students from both McGill University and ETH Zurich.
Additionally, Jiao’s work on the proposed mechanism could help clarify the formation of supermassive black holes, which are central to many massive galaxies and contain millions to billions of solar masses. Brandenberger points out, “A major mystery in cosmology is the origin of the large number of black hole candidates that have been observed at high redshifts.”
Their ongoing research aims to understand how the mechanisms explored could contribute to the conditions necessary for black hole formation, particularly how electromagnetic radiation generated after recombination may prevent fragmentation, allowing matter to collapse into black hole seeds.
This research underscores the interconnectedness of dark matter, magnetic fields, and the fundamental structure of the universe, promising exciting developments in our understanding of cosmological phenomena.
