Webb finds an unusual planet orbiting a pulsar ^{CEFR B2}

Scientists using the James Webb Space Telescope have reported a new kind of exoplanet that challenges standard formation theories. Officially designated PSR J2322-2650b, the body has a mass similar to Jupiter and orbits a rapidly spinning neutron star, or pulsar. The pulsar emits beams of electromagnetic radiation, mainly gamma rays and other high-energy particles, but those emissions are invisible to Webb’s infrared instruments. That allowed a clean spectrum to be obtained and detailed study of the planet throughout its orbit.

The planet’s atmosphere is exotic: it is dominated by helium and carbon, carries soot clouds, and shows molecular carbon species (C2 and C3) rather than the usual water, methane or carbon dioxide. Under the planet’s intense pressure, carbon may condense into diamonds, a result that the team says is difficult to explain and that appears to rule out known formation mechanisms. Brightness models indicate the pulsar’s gravity pulls the companion into a lemon shape.

The system fits the rare “black widow” class, where mass transfer can spin up the pulsar and a strong wind then evaporates the companion. Roger Romani proposed that cooling and crystallization inside the companion could bring pure carbon crystals to the surface, mixing them with helium, but he noted controversy about how oxygen and nitrogen would be kept away. The authors call for further observations and modelling. The discovery was enabled by Webb’s infrared sensitivity, its distant orbit from Earth and its large sunshield; the study is accepted for publication in The Astrophysical Journal Letters, with funding from NASA and the Heising-Simons Foundation.