Accretion, Ablation and Propeller Evolution in Close Millisecond Pulsar Binary Systems

TL;DR

This paper models the formation and evolution of binary millisecond pulsars with low-mass companions, highlighting the roles of accretion, ablation, and propeller mechanisms in producing black widow systems with specific orbital and companion mass characteristics.

Contribution

It introduces a comprehensive population synthesis model that incorporates non-conservative mass loss processes to explain black widow pulsar formation and their observed properties.

Findings

Propeller and ablation mechanisms can produce black widow pulsars from low-mass X-ray binaries.

Predicted orbital periods can reach up to ~0.4 days with companion masses as low as ~0.005 Msun.

The model aligns with observed birth rates of LMXBs and black widow systems.

Abstract

A model for the formation and evolution of binary millisecond radio pulsars in systems with low mass companions (< 0.1 Msun) is investigated using a binary population synthesis technique. Taking into account the non conservative evolution of the system due to mass loss from an accretion disk as a result of propeller action and from the companion via ablation by the pulsar, the transition from the accretion powered to rotation powered phase is investigated. It is shown that the operation of the propeller and ablation mechanisms can be responsible for the formation and evolution of black widow millisecond pulsar systems from the low mass X-ray binary phase at an orbital period of ~0.1 day. For a range of population synthesis input parameters, the results reveal that a population of black widow millisecond pulsars characterized by orbital periods as long as ~0.4 days and companion masses as low as ~0.005 Msun can be produced. The orbital periods and minimum companion mass of this radio millisecond pulsar population critically depend on the thermal bloating of the semi-degenerate hydrogen mass losing component, with longer orbital periods for a greater degree of bloating. Provided that the radius of the companion is increased by about a factor of 2 relative to a fully degenerate, zero temperature configuration, an approximate agreement between observed long orbital periods and theoretical modeling of hydrogen rich donors can be achieved. We find no discrepancy between the estimated birth rates for LMXBs and black widow systems, which on average are $\sim~1.3\times10^{-5} {\rm yr}^{-1}$ and $1.3\times10^{-7} {\rm yr}^{-1}$ respectively.