Impact of Asymmetrical Mass Ejection from Proto-White Dwarfs on the Properties of Binary Millisecond Pulsars

TL;DR

This paper investigates how asymmetrical mass ejection from proto-white dwarfs influences the orbital properties and tilt angles of binary millisecond pulsars, offering explanations for observed eccentricities and tilts.

Contribution

It introduces a simulation study of the impact of asymmetrical mass ejection on BMSPs, supporting the thermonuclear rocket model as a plausible formation mechanism.

Findings

Thermonuclear rocket model can explain eccentric BMSPs and tilt angles.

Predicted orbital periods for eBMSPs range from less than one day to several hundred days.

Simulation results align with observed properties of BMSPs.

Abstract

The standard formation theory of binary millisecond pulsars (BMSPs) predicts efficient orbital circularization due to tidal interaction during the previous mass transfer phase. Therefore, BMSPs are expected to have a circular orbit. However, the discovery of several eccentric BMSPs (eBMSPs) with a white dwarf (WD) companion has challenged this picture. In particular, recent observation reveals that the spin angular momentum of the eBMSP J0955$-$6150 is tilted at an angle $>4.8^{\rm \degree}$ from the orbital angular momentum. This is the first time that a tilt angle is deduced for eBMSPs, which provides an important clue to their formation mechanism. Both the orbital eccentricity and tilt angle could be qualitatively accounted for by asymmetrical mass ejection during thermonuclear flashes from proto-WDs (so-called the thermonuclear rocket model), but detailed studies are still lacking. In this paper, we simulate the impact of the kick caused by asymmetrical mass ejection on the properties of BMSPs. We find that the thermonuclear rocket model can potentially explain the observational characteristics of both eBMSPs and normal BMSPs under reasonable input parameters. In addition, our results predict a wide range of the orbital period (from less than one day to more than several hundred days) for eBMSPs, which can be tested by future observations.