Unveiling the Secrets of Protoplanetary Discs: A Deep Dive into the Flying Saucer's Vertical Structure
The formation of planets is a complex process, and understanding the physical structure of protoplanetary discs is crucial. In a recent study, researchers have used data from the James Webb Space Telescope's NIRSpec instrument as part of the JEDIce program to reveal the vertical structure of the Flying Saucer protoplanetary disc. This disc is particularly intriguing because it is 'back-lit' by an ambient emission region containing Polycyclic Aromatic Hydrocarbons (PAHs).
PAHs, excited by ultraviolet photons, emit infrared photons that are absorbed by the disc at specific wavelengths. This creates a silhouette effect, with the midplane of the disc (where most of the mass and potential planet formation occurs) appearing in contrast to the upper layers. By studying this silhouette, the authors can gain insights into the disc's structure and properties.
To create a comprehensive model, the researchers utilized the RADMC3D radiative transfer model, which simulates the path of light from the disc to the observer. They incorporated the ambient emitting region, light scattered from the star, and a foreground cloud of dust to account for interstellar dust extinction. This model was then combined with the point-spread function of the JWST, and the results were compared to observations.
The findings were impressive. The models closely matched the observations, allowing the authors to infer key properties of the disc's vertical structure. Here's what they discovered:
The Flying Saucer's Radius Mystery: The disc's radius, when considering small grains, is 235 au, which differs from the 190 au radius inferred from millimetre observations using the Atacama Large Millimeter Array (ALMA). This discrepancy highlights the importance of distinguishing between micron-sized dust traced by JWST and larger, millimetre-sized grains traced by ALMA. The cause of this radius difference remains a subject of further investigation.
Settling Behavior of Grains: Smaller grains exhibit less settling compared to larger, millimetre-sized grains. This finding aligns with theoretical expectations, and the authors plan to conduct a follow-up study to thoroughly analyze the disc's structure and properties.
Vertical Extent of Icy Grains: The vertical extent of small, icy grains is larger than anticipated. While forces within the disc's gravity and gas pressure suggest a certain height above the midplane, the models indicate a small fraction of ice-covered dust at even greater heights. However, the authors caution that model parameters might be degenerate, making it challenging to pinpoint the exact contribution of individual parameters in real-world scenarios.
The Flying Saucer offers a unique opportunity to study protoplanetary discs through the polycyclic aromatic hydrocarbon emission. The authors' follow-up study is highly anticipated, as it will provide further insights into the complex processes occurring within these discs.
This research, edited by Mckenzie Ferrari, showcases the power of advanced telescopes like the James Webb Space Telescope in unraveling the mysteries of our universe.
