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Title: Were cosmic magnetic seed fields primordial or astrophysical?
Plain: Dynamos in galaxies can amplify a weak magnetic field, but they need a starting seed. The seed could come from the early universe or from the first stars and galaxies.
Precise: Galaxies and clusters host fields of ~1e-6 G coherent over $\sim 10\,\mathrm{kpc}$, amplified by dynamos from seeds $B_{\mathrm{seed}}$. Identify the origin of the seeds: Biermann battery in the first collapsed structures (~1e-20 G), inflationary magnetogenesis, or first-order phase transitions. An answer identifies the origin through the void field strength, coherence length and helicity, which differ between scenarios.
Settled by: Measured strength, coherence length and helicity of void fields compared with the predictions of each scenario.
Kind: phenomenon
Answer type: identification
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)