Signatures of magnetic flux expulsion from neutron star cores

TL;DR

This paper investigates whether magnetic flux can be expelled from neutron star cores during superconductivity onset, revealing new evolutionary pathways and potential observable signals like radio bursts and gravitational waves.

Contribution

It demonstrates that incomplete flux expulsion leads to novel neutron star evolution models, explaining certain transient phenomena and linking magnetic reconnection to gravitational wave signals.

Findings

Partial flux expulsion can produce long-period radio transients.

Reconnection at superconductivity onset may generate detectable gravitational waves.

New evolutionary branches explain properties of older neutron stars.

Abstract

Shortly after a neutron star is born, the protons in its core begin to form a superconductor. In terrestrial materials, the hallmark of superconductivity is an associated expulsion of magnetic flux, but whether this expulsion process can be effective in neutron stars remains an open question -- one with major implications for the phenomenology of pulsars and magnetars. Earlier theoretical arguments suggested flux must be trapped within the core, yet models of magnetars rely on it being expelled from the core and confined to the crust, where it can evolve on kyr timescales. We show that if expulsion is not complete, a qualitatively new evolutionary branch for neutron stars arises, which can account for the properties of newly discovered long-period radio transients and fast radio bursts in older environments. One recently proposed model that could create such field topologies has additional implications for gravitational wave emission and predicts a characteristic energy release that, if observed, will corroborate the role of reconnection at the onset of superconductivity and can constrain the superconducting proton gap.