Electrodynamics and dissipation in the binary magnetosphere of pre-merger neutron stars

TL;DR

This study uses 3D force-free electrodynamics simulations to explore energy dissipation mechanisms in binary neutron star magnetospheres, revealing complex interactions, instabilities, and potential electromagnetic signals prior to merger.

Contribution

It provides the first detailed analysis of magnetospheric interactions, including instabilities and energy release processes, in binary neutron star systems with various magnetic inclinations.

Findings

Aligned systems develop separatrix current sheets and dissipation regions.

Kelvin-Helmholtz instability drives significant magnetospheric dissipation.

Inclined systems emit Alfvénic turbulence and fast magnetosonic waves.

Abstract

We investigate energy release in the interacting magnetospheres of binary neutron stars (BNSs) with global 3D force-free electrodynamics simulations. The system dynamics depend on the inclinations $\chi_1$ and $\chi_2$ of the stars' magnetic dipole moments relative to their orbital angular momentum. The simplest aligned configuration ($\chi_1=\chi_2=0^\circ$) has no magnetic field lines connecting the two stars. Remarkably, it still develops separatrix current sheets warping around each star and a dissipative region at the interface of the two magnetospheres. A Kelvin-Helmholtz (KH)-type instability drives significant dissipation at the magnetospheric interface, generating local Alfv\'enic turbulence and escaping fast magnetosonic waves. Binaries with inclined magnetospheres release energy in two ways: via KH instability at the interface and via magnetic reconnection flares in the twisted flux bundles connecting the companions. Outgoing compressive waves occur in a broad range of BNS parameters, possibly developing shocks and sourcing fast radio bursts. We discuss implications for X-ray and radio precursors of BNS mergers.