JWST discovers planet with all-carbon atmosphere orbiting 'black widow' star

A rendering that is part of an animation of the Black Widow pulsar burning up its companion. (Image credit: NASA Goddard Spaceflight Center/Cruz deWilde)

Science advances based on data that doesn’t fit our current understanding. At least, that was the theory of Thomas Kuhn in his famous paper “On the Structure of Scientific Revolutions.” Scientists should therefore welcome new data that challenges their understanding of the universe. A recent paper, available as a preprint on arXiv, using data from the James Webb Space Telescope (JWST) may have found data that could help. It looked at an exoplanet orbiting a millisecond pulsar and found that its atmosphere was made almost entirely of pure carbon.

This type of pulsar, PSR J2322-2650, is known as a “black widow” system because it fuels its high-energy emissions by gobbling up material from a nearby star. In this case, that nearby star has likely degraded into a “hot Jupiter”-type companion planet that orbits its neutron star every 7.8 hours. The typical process of forming a black widow involves two stages: first, the neutron star (which in this case is also a pulsar) gobbles up material, and then, second, it blasts its companion with high-energy gamma rays, stripping away much of the companion’s outer layers and creating a Jupiter-sized, helium-dominated exoplanet.

The exoplanet orbiting PSR J2322-2650, known as PSR J2322-2650b, does indeed fit the description of a Jupiter-sized planet that appears to have the same density as would be expected if it were composed primarily of helium. However, its atmosphere is unlike any other black widow companion planet ever observed. According to JWST spectrographic data, its atmosphere is composed primarily of elemental carbon in the form of tricarbon (C3) or dicarbon (C2).