Compact millisecond pulsar (MSP) binaries are crucial for understanding the formation of massive pulsars and the boundary between neutron stars (NSs) and black holes (BHs). Often referred to as “spiders” due to the cannibalistic interaction between the pulsar and its companion, these systems are broadly categorized into redbacks (RBs, with companion masses between 0.1 and 0.5 solar masses) and black widows (BWs, with companion masses below 0.1 solar masses). These binaries originate from X-ray binaries, where the NS accretes material from its companion, spinning up to millisecond periods.
In our work, we simulate binary systems comprising a neutron star and a companion star, incorporating detailed physical processes such as accretion-induced spin-up, pulsar wind irradiation, and magnetic field evolution. The simulations confirm that spider binaries evolve from low- and intermediate-mass X-ray binaries, with RBs transitioning into compact BWs as the pulsar wind strips the companion star.
We also investigate “huntsman spiders”, with wider orbits than typical spiders, concluding that they are unlikely to produce the most massive NSs. Efficient mass transfer and strong pulsar wind irradiation account for many observed properties of Galactic spider pulsars, including the absence of hydrogen in some companions and the orbital period distribution of spiders. Our results emphasize that spider evolutionary pathways depend critically on factors such as the efficiency of accretion, the strength of the pulsar wind, and the initial binary configuration. Additionally, we show that accreting significant mass can lead to NS collapse into a BH before achieving sub-millisecond spin periods, providing key insights into the upper limits of pulsar spin rates.
