Unveiling the Secrets of Carbon-rich Chemistry in a Transitional Disk: A JWST Discovery
The James Webb Space Telescope (JWST) has made a groundbreaking discovery, revealing a hidden world of carbon-rich chemistry in a transitional disk. This finding not only expands our understanding of planet-forming environments but also challenges our assumptions about the role of accretion rates and dust grains in shaping these environments.
The study, led by Máire Volz and her team, focused on two Classical T Tauri stars, GM Aur and RX J1615.3-3255 (J1615). These stars, both hosting transitional disks, were observed using the JWST's Medium Resolution Spectrometer (MRS).
Despite their similar stellar and disk properties, the two systems displayed striking differences in their carbon-bearing molecular emission. By analyzing spectral lines within the 13.6-17.7 micron wavelength range, the team found that J1615 exhibited strong emission from H2O, HCN, C2H2, 12CO2, 13CO2, OH, and 13C12CH2, while GM Aur showed only H2O and OH.
The enhanced carbon emission in J1615 may result from a combination of lower accretion rate and larger and more processed dust grains in the inner disk. These conditions allow carbon-rich gas to persist and be detected, providing new insights into the chemical diversity of planet-forming environments.
The team also measured the accretion rates of both objects using contemporaneous optical spectra and found that J1615's accretion rate is lower than that of GM Aur. They constrained the properties of the dust in both disks using SED modeling and found elevated amounts of crystalline silicates and larger dust grains in the disk of J1615.
This discovery expands the sample of protoplanetary disks around solar-mass stars with strong CO2 and C2H2 emission and identifies J1615 as a carbon-rich transitional disk. It invites further exploration of the chemical diversity of planet-forming environments and challenges our assumptions about the role of accretion rates and dust grains in shaping these environments.
This research was published in the Astrophysical Journal and accepted on November 11, 2025. It provides a fascinating insight into the complex interplay between stellar and disk properties and the chemical processes that shape planet-forming environments.
