Tiny, highly uniform magnetic fields extend across the universe, influencing various cosmic processes. Despite their significance, the mechanisms behind the generation of these fields have remained elusive. Recent research from a collaboration between McGill University and ETH Zurich has proposed a new mechanism that may explain how cosmological magnetic fields arise, as detailed in a paper published in the journal Physical Review Letters on February 15, 2026.
The study focuses on a quantum field, known as a pseudo-scalar field, which could give rise to ultralight dark matter. This type of dark matter consists of particles that possess very low mass and interact weakly with ordinary matter. According to co-authors Robert Brandenberger and Jurg Frohlich, along with their colleague Hao Jiao, the concept of dark matter has been supported by various astronomical observations, though its exact composition remains unknown.
Brandenberger explained, “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 research builds upon earlier studies conducted in 1997, 2000, and 2012 that explored similar phenomena.
Parametric Resonance and Magnetic Field Generation
The researchers examined the concept of parametric resonance, a phenomenon where fields grow exponentially when coupled to an oscillating source. With renewed interest in ultralight dark matter, particularly concerning a field known as an axion, they proposed that this oscillating field could serve as a source for the amplification of electromagnetic fields.
Brandenberger and Frohlich elaborated, “We immediately realized that 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.” Their calculations suggest that the mechanism could generate magnetic fields sufficient to explain existing observations.
The authors focus on conditions in the universe following a critical period known as recombination, which occurred approximately 380,000 years after the Big Bang. During this time, the universe cooled enough for electrons and nuclei to form neutral atoms, allowing magnetic fields to persist for extended periods.
Their approach uses an interaction term that couples the pseudo-scalar axion field to the electromagnetic field, demonstrating that this interaction can produce significant magnetic field growth sourced from oscillating axion fields.
Implications for Cosmology and Future Research
Brandenberger and Frohlich assert that their findings challenge previous assumptions in astrophysical theories. They noted, “Before our work, it was considered very unlikely that magnetic fields on cosmological scales surviving until the present are generated at late times.” Their research suggests that existing magnetic fields could have formed without invoking new physics from the early universe.
While the study shows promise, the researchers recognize the need for deeper investigation into specific aspects of their mechanism. Brandenberger stated, “For example, we need to study how the magnetic fields generated according to our mechanism back-react on dark matter.” Understanding the energy density conversion from dark matter to electromagnetic energy density will be crucial in validating their findings.
Additionally, the team aims to explore magnetic field generation before recombination, when plasma dynamics play a significant role. This exploration may require numerical simulations, potentially conducted by students at both McGill University and ETH Zurich.
A particularly intriguing line of inquiry from Hao Jiao examines how their proposed mechanism for generating electromagnetic radiation could enhance understanding of supermassive black hole formation. These black holes, which contain hundreds of thousands to billions of solar masses, 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.”
The researchers posit that the mechanism could facilitate a sufficient flux of Lyman-Werner photons, preventing gas fragmentation necessary for black hole seed formation. This line of research may yield significant insights into the complexities of cosmic evolution and structure formation.
The findings from Brandenberger, Frohlich, and Jiao offer a fresh perspective on the relationship between dark matter and cosmological magnetic fields. As investigations continue, their work may pave the way for a deeper understanding of the universe’s fundamental components and the processes that shape its evolution.
