Dynamical Effects of Colliding Outflows in Binary Systems

TL;DR

This study uses 3D hydrodynamic simulations to explore how colliding outflows in binary systems influence orbital dynamics, revealing that dense, slow outflows can cause orbit expansion through positive gravitational torque.

Contribution

It provides the first global 3D simulation analysis of dynamical anti-friction effects in binary systems with colliding outflows, demonstrating orbit expansion mechanisms.

Findings

Dense, slow outflows induce positive torque and orbit expansion.

Gravitational force drops as O(r^{-3}), ensuring convergence.

Binaries with AGB stars and pulsars can experience ~10% orbit increase.

Abstract

The outflow of an object traveling in a fluid can shape the fluid morphology by forming a forward bow shock which accelerates the object via gravitational feedback. This dynamical effect, namely "dynamical anti-friction", has been studied in idealized infinite uniform media, which suffers from the convergence problem due to the long-range nature of gravitation. In this work, we conduct global 3D hydrodynamic simulations to study this effect in the scenario of a binary system, where the collision of outflows from both stars creates a suitable configuration. We demonstrate with simulations that a dense and slow outflow can give rise to a positive torque on the binary and lead to the expansion of the orbit. As an application, we show that binaries consisting of an AGB star and an outflowing pulsar can experience $\sim 10~\%$ orbit expansion during the AGB stage, in addition to the contribution from mass-loss. We also prove that the gravitational force drops as $O(r^{-3})$ from the center of mass in the binary scenarios, which guarantees a quick converge of the overall effect.