2025ApJ...995L..64Z

A handful of enigmatic Jupiter-mass objects have been discovered orbiting pulsars. One such object, PSR J2322-2650b, uniquely resembles a hot-Jupiter exoplanet, due to its minimum density of 1.8 g cm^–3 and its ∼1900 K equilibrium temperature. We use JWST to observe PSR J2322-2650b's emission spectrum across an entire orbit. In stark contrast to every known exoplanet orbiting a main-sequence star, we find an atmosphere rich in molecular carbon (C₃, C₂) with strong westward winds. Our observations open up new exoplanetary chemical (ultrahigh C/O and C/N ratios of >100 and >10,000, respectively) and dynamical regimes (ultrafast rotation with external irradiation) to observational study. The extreme carbon enrichment poses a severe challenge to the current understanding of “black-widow” companions, which were expected to consist of a wider range of elements due to their origins as stripped stellar cores.