Electrodynamics and Dissipation in the Binary Magnetosphere of Premerger Neutron Stars

Abstract

We investigate the 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 χ1 and χ2 of the stars’ magnetic dipole moments relative to their orbital angular momentum. The simplest aligned configuration (χ1 = χ2 = 0∘) 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 Alfvénic 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.