Josephson currents in neutron stars

TL;DR

This paper explores how superfluid interfaces in neutron stars induce Josephson-like currents, leading to radiation and heating effects that impact the star's thermal evolution.

Contribution

It introduces a novel mechanism of supercurrent induction at superfluid interfaces in neutron stars, including dynamic effects and associated radiation.

Findings

Neutron supercurrents are induced at S-wave and P-wave superfluid interfaces.

Motion of vortex lines causes oscillating Josephson currents and radiation.

Radiation power exceeds neutron star Ohmic dissipation, affecting star cooling.

Abstract

We demonstrate that the interface between $S$-wave and $P$-wave paired superfluids in neutron stars induces a neutron supercurrent, a charge-neutral analog of the Josephson junction effect in electronic superconductors. The proton supercurrent entrainment by the neutron superfluid generates, in addition to the neutral supercurrent, a charged current across the interface. Beyond this stationary effect, the motion of the neutron vortex lines responding to secular changes in the neutron star's rotation rate induces a time-dependent oscillating Josephson current across this interface when proton flux tubes are dragged along with them. We show that such motion produces radiation from the interface once clusters of proton flux tubes intersect the interface. The power of radiation exceeds by orders of magnitude the Ohmic dissipation of currents in neutron stars. This effect appears to be phenomenologically significant enough to heat the star and alter its cooling rate during the photon cooling era.