Magnetic fields from cosmological bulk flows

TL;DR

This paper investigates how cosmological bulk flows could generate seed magnetic fields in the early universe through the Harrison mechanism, potentially explaining the origin of cosmic magnetism.

Contribution

It demonstrates that matter bulk flows within current observational limits can produce sufficient seed magnetic fields for galaxy formation.

Findings

Bulk flows can generate magnetic fields of 10^{-21} G on 10 kpc scales.

Generated magnetic fields could seed galactic dynamos.

Results are consistent with Planck constraints on bulk flow velocities.

Abstract

We explore the possibility that matter bulk flows could generate the required vorticity in the electron-proton-photon plasma to source cosmic magnetic fields through the Harrison mechanism. We analyze the coupled set of perturbed Maxwell and Boltzmann equations for a plasma in which the matter and radiation components exhibit relative bulk motions at the background level. We find that, to first order in cosmological perturbations, bulk flows with velocities compatible with current Planck limits ($\beta<8.5\times 10^{-4}$ at $95\%$ CL) could generate magnetic fields with an amplitude $10^{-21}$ G on 10 kpc comoving scales at the time of completed galaxy formation which could be sufficient to seed a galactic dynamo mechanism.