Magnetar field dynamics shaped by chiral anomalies and helicity

TL;DR

This paper demonstrates how the chiral magnetic effect influences magnetar magnetic field evolution, leading to rapid amplification of large-scale magnetic fields within a century through a novel CME-driven mechanism.

Contribution

It introduces a new CME-based mechanism for magnetar magnetic field reconfiguration, distinct from traditional dynamo models, supported by 3D magneto-thermal simulations.

Findings

Magnetic helicity sustains chiral asymmetry without external energy.

Large-scale magnetic fields (>10^14 G) are amplified within a century.

Small-scale magnetic structures are diminished during amplification.

Abstract

The chiral magnetic effect (CME) -- a macroscopic manifestation of the quantum chiral anomaly -- induces currents along magnetic field lines, facilitating mutual conversion between chiral asymmetry and magnetic helicity. Although the finite electron mass suppresses chiral asymmetry through spin-flip processes, we demonstrate that the CME effectively shapes magnetar field evolution. Magnetic helicity acts as a persistent internal source of chiral asymmetry, which mediates the redistribution of magnetic energy across spatial scales, without requiring an external energy source. Our three-dimensional magneto-thermal simulations of the neutron star crust reveal a novel mechanism that significantly reconfigures the magnetic field inherited at birth, amplifying both toroidal and poloidal large-scale dipolar components (crucial for spin-down) to strengths of >1e14 G within just a century, at the expense of small-scale structures. This astrophysical application of the CME, distinct and complementary to conventional hydrodynamic dynamo models, offers an innovative framework for understanding magnetar field dynamics and provides a transformative solution to the origin of their exceptionally strong, large-scale fields.