Ultraviolet “winds” erode a young star’s protoplanetary disk in Orion Nebula

Ultraviolet “winds” from nearby massive stars are stripping the gas from a young star’s protoplanetary disk, causing it to rapidly lose mass, according to a new study. It reports the first directly observed evidence of far-ultraviolet (FUV)-driven photoevaporation of a protoplanetary disk. The findings, which use observations from the James Web Space Telescope (JWST), provide new insights into the constraints of gas giant planet formation, including in our own Solar System. Young low-mass stars are often surrounded by relatively short-lived protoplanetary disks of dust and gas, which provide the raw materials from which planets form. As such, gas giant planet formation is limited by processes that remove mass from protoplanetary disks, such as photoevaporation. Photoevaporation occurs when the upper layers of protoplanetary disks are heated by x-ray or ultraviolet protons, which increases the gas temperature and causes it to escape from the system. Since most low-mass stars form in clusters also containing massive stars, protoplanetary disks are expected to be exposed to external radiation and experience ultraviolet-driven photoevaporation. Theoretical models predict that far-ultraviolet radiation produces photodissociation regions (PDRs) – areas where ultraviolet photons cast by nearby massive stars strongly influence gas chemistry on the surfaces of protoplanetary disks. However, direct observation of these processes has been elusive. Using near-infrared and submillimeter measurements from the JWST and the Atacama Large Millimeter Array, respectively, Olivier Berné and colleagues report observations of a FUV-irradiated protoplanetary disk, d203-506, located inside the Orion Nebula. By modeling the kinematics and excitation of the emission lines detected within the PDR, Berné et al. found that d203-506 is losing mass at a high rate due to FUV-driven heating and ionization. According to the findings, the rate at which this mass is being lost from d203-506 indicates that the gas could be removed from the disk within a million years, suppressing the ability for gas giants to form within the system. “Dynamical and compositional studies of the Solar System indicate that it formed in a stellar cluster that contained one or more massive stars, and so it might have been affected by FUV radiation,” Berné et al. write.