Cosmological Magnetic Fields and Their Evolution
Summary
Magnetic fields pervade the Universe, from galaxies and clusters to the vast intergalactic medium. Their genesis—magnetogenesis—may trace back to processes in the early Universe such as inflationary fluctuations or phase transitions, or to later astrophysical dynamos operating in protogalaxies and active galactic nuclei. Once generated, these fields evolve under the combined influences of cosmic expansion, magnetohydrodynamic turbulence and reconnection, often exhibiting inverse cascades that transfer magnetic energy from small to large scales. Observational probes include Faraday rotation of polarised radio sources, imprints on the cosmic microwave background and the deflection of secondary gamma-ray cascades from distant blazars. Numerical simulations now couple cosmological structure formation with magnetic feedback, revealing roles for seed fields in regulating star formation, cosmic-ray propagation and even subtle effects on the Hubble expansion rate. A coherent picture is emerging in which primordial relics and astrophysical amplifiers jointly shape the present-day magnetic landscape, with implications for galaxy evolution, high-energy astrophysics and fundamental cosmology.
Research from Nature Portfolio
Recent studies propose that the decay of primordial fields generated at the electroweak phase transition can proceed via magnetic reconnection that conserves helicity fluctuations. This mechanism yields relic intergalactic fields several orders of magnitude stronger than earlier estimates, restoring compatibility with gamma-ray observations of cosmic voids and providing seed fields for galaxy clusters. By linking electroweak-scale magnetogenesis to present-day field strengths, this work also offers a novel route to alleviating the Hubble tension through magnetic effects at recombination.
Cosmological Magnetic Fields and Their Evolution publication trend
The graph below shows the total number of articles in cosmological magnetic fields and their evolution across all publications each year (not limited to Nature Index journals).
Technical terms
Magnetogenesis: Processes in the early Universe or in astrophysical objects that generate initial magnetic fields.
Magnetic helicity: A measure of the twist and linkage of magnetic field lines, approximately conserved under ideal magnetohydrodynamics.
Inverse cascade: Transfer of magnetic energy from smaller to larger spatial scales during turbulent evolution.
Coherence length: The typical scale over which a magnetic field remains directionally correlated.
Faraday rotation: Rotation of the plane of polarisation of electromagnetic waves propagating through a magnetised plasma.
References
- Cosmic-void observations reconciled with primordial magnetogenesis. Nature Communications (2023).
- Constraints on the Intergalactic Magnetic Field Using Fermi-LAT and H.E.S.S. Blazar Observations. The Astrophysical Journal Letters (2023).
- A lower bound on intergalactic magnetic fields from time variability of 1ES 0229+200 from MAGIC and Fermi/LAT observations. Astronomy & Astrophysics (2023).
- Constraining the Astrophysical Origin of Intergalactic Magnetic Fields. The Astrophysical Journal (2024).
- The Turbulent Chiral Magnetic Cascade in the Early Universe. The Astrophysical Journal Letters (2017).
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