Orbital evolution of colliding star and pulsar winds in 2D and 3D; effects of: dimensionality, EoS, resolution, and grid size

TL;DR

This study uses 2D and 3D relativistic hydrodynamic simulations to analyze the complex, turbulent interactions of stellar and pulsar winds in binary systems, revealing the effects of dimensionality, equation of state, resolution, and grid size on shock structures and instabilities.

Contribution

First 3D simulations of isotropic stellar and pulsar wind interactions along a full orbit, exploring effects of resolution, grid size, and different equations of state.

Findings

3D simulations show faster instability growth and more turbulence.

Higher resolution confirms stability results; larger grids show loss of global coherence.

Multiple instabilities (KHI, Richtmyer-Meshkov, RTI) influence flow evolution.

Abstract

(abridged)The structure formed by the shocked winds of a massive star and a non-accreting pulsar in a binary suffers periodic and random variations of orbital and non-linear dynamical origin. For the 1st time, we simulate in 3 D the interaction of isotropic stellar and relativistic pulsar winds along 1 full orbit, on scales well beyond the binary size. We also investigate the impact of grid resolution and size, and of different EoOs: a gamma-constant ideal gas, and an ideal gas with gamma dependent on temperature. We carry out, with the code PLUTO, relativistic HD simulations in 2 and 3 D of the interaction of a slow wind and a relativistic wind with Gamma=2 along 1 full orbit up to ~100 x the binary size. The different 2-D simulations are carried out with equal and larger grid resolution and size, and 1 of them is done with a more realistic equation of state, than in 3 D. The simulations in 3 D confirm previous results in 2 D. The shocked flows are subject to a faster instabilities growth in 3 D, which enhances the presence of shocks, mixing, and large-scale disruption. In 2 D, higher resolution simulations confirm lower resolution results, simulations with larger grid sizes strengthen the case for the loss of global coherence of the shocked-wind structure, and simulations with 2 different EoOs yield very similar results. In addition to the KHI, we find that the Richtmyer-Meshkov and the RTI are likely acting together in the shocked flow evolution. Simulations in 3 D confirm that the interaction of stellar and pulsar winds yields structures that evolve non-linearly and get strongly entangled. The evolution is accompanied by strong kinetic energy dissipation, rapid changes in flow orientation and speed, and turbulent motion. The results strengthen the case for the loss of global coherence of the shocked structure on large scales, although higher pulsar wind speed simulations are needed.