What can we say about seed fields for galactic dynamos?

TL;DR

This paper argues that a quasi-uniform cosmological seed field is inadequate for galactic dynamo models within the universe's age, challenging previous assumptions and suggesting modifications to galactic magnetic field evolution scenarios.

Contribution

It demonstrates the limitations of conventional seed fields for galactic dynamos and explores the implications of larger dynamo numbers on magnetic field development.

Findings

Conventional cosmological seed fields are insufficient for galactic dynamo amplification within the universe's age.

Larger dynamo numbers could alter the efficiency and timescale of magnetic field growth.

The results prompt reconsideration of initial conditions in galactic magnetic field models.

Abstract

We demonstrate that a quasi-uniform cosmological seed field is a much less suitable seed for a galactic dynamo than has often been believed. The age of the Universe is insufficient for a conventional galactic dynamo to generate a contemporary galactic magnetic field starting from such a seed, accepting conventional estimates for physical quantities. We discuss modifications to the scenario for the evolution of galactic magnetic fields implied by this result. We also consider briefly the implications of a dynamo number that is significantly larger than that given by conventional estimates.