Generation of strong magnetic fields in old neutron stars accounting for continuous chiral magnetic effect

TL;DR

This paper introduces a new mean field dynamo model in anomalous MagnetoHydroDynamics that explains the generation of extremely strong magnetic fields in old neutron stars through the continuous chiral magnetic effect, despite rapid spin-flip processes.

Contribution

The paper presents a novel nonlinear dynamo model in AMHD that accounts for sustained chiral magnetic effects in old neutron stars, differing from traditional models by considering ongoing chiral imbalance evolution.

Findings

Magnetic fields in old neutron stars can reach over 10^{18} G.

The model demonstrates continuous chiral magnetic effect despite rapid spin-flip.

Magnetic fields are amplified from seed fields due to previous stellar evolution stages.

Abstract

We suggest a new mean field dynamo model in anomalous MagnetoHydroDynamics (AMHD) accounting for the mean spin (polarization) of the magnetized chiral (ultrarelativistic) plasma of a neutron star (NS). For simplicity we consider a non-superfluid NS with its rigid rotation neglecting also any matter turbulence (convection) within a star. On this way, we recover the Chiral Magnetic Effect (CME) as a possible source for the amplification of a seed, sufficiently strong magnetic field, $B\sim 10^{13}\,\text{G}$, up to values $B\gtrsim 10^{18}\,\text{G}$ in old NS's, having ages $t\gtrsim 10^6\,\text{yr}$. The important issue in AMHD model suggested is the continuous evolution of the chiral imbalance providing the CME for these ages, $\partial_t\mu_5 (t)\neq 0$, in spite of the fast spin-flip in Coulomb collisions in the dense NS plasma that leads to vanishing $\mu_5\to 0$ at an earlier epoch in the corresponding protoneutron star. In contrast to the conventional mean-field dynamos, the dynamo drivers in the model are produced due to magnetic field generated at the previous stages of stellar evolution. It makes our model basically nonlinear.