Generation of Seed Magnetic Fields in Primordial Supernova Remnants

TL;DR

This study investigates how seed magnetic fields are generated in primordial supernova remnants through the Biermann mechanism, highlighting the importance of electron-ion temperature relaxation and providing estimates of magnetic field strengths relevant for galaxy formation.

Contribution

The paper presents the first detailed 2D MHD simulations of magnetic field generation in early supernova remnants considering electron-ion temperature relaxation effects.

Findings

Magnetic energy generated reaches about 10^26 erg in SNRs.

Magnetic fields of ~10^-19 G are estimated in protogalaxies.

The analytic expression for magnetic energy agrees with numerical results.

Abstract

Origin of the magnetic field ubiquitous in the Universe is studied based on the Biermann mechanism, which is expected to work in the non-barotropic region. We perform a series of two-dimensional MHD simulations of the first generation supernova remnant (SNR) expanding in the inhomogeneous interstellar matter (ISM) and study the Biermann mechanism working in the interior of the SNR. Especially, we pay attention to the relaxation process of electron and ion temperatures via the Coulomb interaction. In the early SNR in which the electron temperature is much lower than the ion temperature, the Biermann mechanism is ineffective, since the gradient of electron pressure is small. Magnetic fields begin to be generated just behind the shock front when the electron temperature is sufficiently relaxed. Assuming the explosion energy of 10^52 erg, the total magnetic energy generated reaches about 10^26 erg and does not depend strongly on the parameters of either SNR or ISM. Analytic expression to estimate the magnetic total energy is presented and it is shown this agrees well with our numerical results. Finally we evaluate the expected amplitude of magnetic fields in protogalaxies as ~10^-19 G, which is sufficient for seed fields of the observed galactic magnetic fields.