2025/11/21 by Hang Gong, Alexey Bobrick, Gong, Hang +17
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Pulsars and Gravitational Waves Research
paper · pdf · doi:10.48550/arxiv.2511.17248
openalex publication_date 2025/11/21 · openalex created_date 2025/11/25 · openalex updated_date 2026/07/28
We present the results of deep near-infrared imaging of the recently discovered helium star pulsar binary J1928+1815 situated in the Galactic plane. Our observations did not achieve significant detections, providing limiting magnitudes of J=23.7 and H=22.2, which are both 2.4 magnitudes deeper than the expected J and H magnitudes for a modeled stripped helium star with a mass of 1 \rm M\odot after extinction. Although we cannot completely rule out the possibility of more significant extinction and the exact evolutionary status of the supposed helium star is uncertain, by comparing J1928+1815 with other pulsar binaries, we propose a natural alternative solution: that J1928+1815 is a heavyweight black widow system with a massive ablated white dwarf. Due to the pulsar's relatively high spin-down power and short orbital separation, the irradiation heating timescale is uniquely shorter than the cooling timescale for the WD companion. As a result, the WD effectively boils, with its outer layers expanding, overfilling the Roche lobe and producing low-density binary-scale haze opaque in the radio band. If this interpretation is correct, J1928+1815 would represent a new category distinct from canonical lightweight black widow systems. Radio eclipses can occur in pulsar binaries across a wider range of WD companion masses than previously thought. Therefore, they do not serve as a definitive indicator of a helium star without its direct detection. We contend that a spectroscopic identification remains the smoking gun for its existence. Given the crowding in this field, an HST imaging in the near-infrared band would provide even better constraints.