The Connection Between Low-Mass X-ray Binaries and (Millisecond) Pulsars: A Binary Evolution Perspective

TL;DR

This paper reviews the evolutionary links between low-mass X-ray binaries and millisecond pulsars, analyzing how different binary evolution pathways produce various observed populations and identifying gaps in current understanding.

Contribution

It provides a detailed binary evolution framework connecting LMXBs and pulsars, highlighting the specific conditions leading to different end-states and identifying unexplained pulsar sub-populations.

Findings

Accreting millisecond pulsars are linked to only two of four LMXB classes.

Most LMXB classes do not have clear pulsar progeny.

Current models explain some pulsar populations but not all.

Abstract

I review the evolutionary connection between low-mass X-ray binaries (LMXBs) and pulsars with binary companions (bPSRs) from a stellar binary evolution perspective. I focus on the evolution of stellar binaries with end-states consisting of a pulsar with a low-mass (<1.0 solar mass) companion, starting at the point the companion's progenitor first initiates mass transfer onto the neutron star. Whether this mass transfer is stable and the physics driving ongoing mass transfer partitions the phase space of the companions's initial mass and initial orbital period into five regions. The qualitative nature of the mass-transfer process and the binary's final end-state differ between systems in each region; four of these regions each produce a particular class of LMXBs. I compare the theoretical expectations to the populations of galactic field LMXBs with companion-mass constraints and field bPSRs. I show that the population of accreting millisecond pulsars are all identified with only two of the four LMXB classes and that these systems do not have readily identifiable progeny in the bPSR population. I discuss which sub-populations of bPSRs can be explained by binary evolution theory and those that currently are not. Finally I discuss some outstanding questions in this field.