The massive magnetic fields found in the empty voids of space cannot be explained by ultralight dark matter after all.
April 23, 2026
Original Paper
Suppressed Magnetogenesis from Ultralight Dark Matter due to Finite Conductivity
arXiv · 2604.17230
The Takeaway
Cosmic voids are the largest empty spaces in the universe, yet they are filled with weak magnetic fields. A recent theory suggested that ultralight dark matter could amplify these fields to their current strength. This study proves that the finite electrical conductivity of the plasma in these voids actually kills that amplification process. The dark matter mechanism simply cannot overcome the dampening effects of the surrounding environment. This finding effectively restarts the search for where the magnetism of the universe's emptiest regions comes from. It rules out a major candidate for the origin of cosmic structure.
From the abstract
Recently, a mechanism for generating astrophysically relevant magnetic fields via ultralight pseudoscalar dark matter, through the coupling term $g_{\phi \gamma} \phi F_{\mu \nu}\tilde{F}^{\mu\nu}$ in the Lagrangian density, was proposed in Brandenberger et al (2026) (see Ref. 1). In this scenario, the electromagnetic fields are amplified through the phenomena of parametric resonance due to the oscillatory behaviour of the pseudoscalar field. However, the analysis presented in that work does not