Spiders are eclipsing millisecond pulsar binaries in which the pulsar ablates its low-mass companion; they are classified as black widows or redbacks based on companion mass. PSR J1932+2121 is a recently discovered Galactic-field redback millisecond pulsar (MSP) with a spin period of 14.2 ms, significantly slower than other known redbacks, and an unusually high surface magnetic field of about 2×10⁹ G. Using detailed binary evolution models, we show that this system likely experienced accretion efficiencies in the range 30 to 50%, that is only 30 to 50% of the material transferred to the pulsar was accreted by it and rest was lost. Hence, PSR J1932 underwent a very inefficient mass-transfer phase, when compared to typical spiders (with accretion efficiencies around 70%) leading to incomplete spin-up during Roche-lobe overflow. It is expected that as the pulsar accretes matter, its surface magnetic field should decrease. Our simulations constrain the progenitor orbital period to 2.0 to 2.6 days and find that standard prescriptions for accretion-induced magnetic field decay cannot account for the high residual field. The system’s companion mass (0.12 solar masses), compact orbit (its orbital period is around 0.08 day) and signs of companion ablation from radio eclipses support its classification as a redback. PSR J1932+2121 offers a unique observational constraint on the limits of pulsar recycling and challenges current models of magnetic field evolution and mass transfer in close binaries.
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Looking for Super-Massive Neutron Stars
