The First Magnetic Fields

TL;DR

This paper reviews the origins of cosmic magnetic fields, discussing observational constraints, primordial generation mechanisms during early universe phases, and astrophysical processes, highlighting their implications for galaxy formation and early cosmic epochs.

Contribution

It provides a comprehensive overview of both primordial and astrophysical mechanisms for magnetic field generation and their impact on early universe phenomena.

Findings

Observations constrain magnetic field strength during galaxy formation.

Primordial mechanisms include inflation and phase transitions.

Astrophysical processes like Biermann battery generate fields after recombination.

Abstract

We review current ideas on the origin of galactic and extragalactic magnetic fields. We begin by summarizing observations of magnetic fields at cosmological redshifts and on cosmological scales. These observations translate into constraints on the strength and scale magnetic fields must have during the early stages of galaxy formation in order to seed the galactic dynamo. We examine mechanisms for the generation of magnetic fields that operate prior during inflation and during subsequent phase transitions such as electroweak symmetry breaking and the quark-hadron phase transition. The implications of strong primordial magnetic fields for the reionization epoch as well as the first generation of stars is discussed in detail. The exotic, early-Universe mechanisms are contrasted with astrophysical processes that generate fields after recombination. For example, a Biermann-type battery can operate in a proto-galaxy during the early stages of structure formation. Moreover, magnetic fields in either an early generation of stars or active galactic nuclei can be dispersed into the intergalactic medium.