How Super-Jupiters are fed: Resolved 3D simulations of gas accretion onto giant planets and line-emission predictions

• Applicant: Dr. Gabriel-Dominique Marleau
• Subject Area: Astrophysics and Astronomy
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553699646

A handful planets of several times Jupiter's mass have been observed while they are currently accreting, that is, gaining mass. They reveal this by characteristic radiation, mainly line transitions of neutral hydrogen, with H alpha the strongest. The ultimate reservoir of the gas is the so-called protoplanetary disc around the young star. The planet is orbiting along with the gas around the star and it is not yet entirely clear how exactly a part of the gas goes from orbiting the star to hitting the planet's surface. Many simulations have partially addressed this but because of limited computational resources, they often "smooth", that is, weaken, the gravity of the planet close to its surface. This is acceptable for their primary goals but it changes heavily the gas flow, slowing it down closest to the planet, where in reality the lines would be emitted. To predict this faithfully, simulations with the non-smoothed gravity of the planet are needed. We have been running such simulations in "(side-view) 2D", i.e., assuming axial symmetry around the planet. However, the accretion process is not symmetric: gas from different directions has different amounts of rotational speed around the planet. Therefore, we propose to run high-resolution, smoothing-free 3D radiation-hydrodynamical simulations of the accretion onto gas giants. This will fill a gap in the simulation landscape. Our experience has prepared us well to address the numerical challenges, and we will benefit from synergies in the research group, namely ongoing 3D simulations of accreting Super-Earths and continued code development. We will vary the input physical quantities to scan the parameter space that applies to existing and upcoming detections. Important outputs include the amount of and the speed of the gas that lands on or close to the planet, or the accretion heating of the local disc, with possible changes to the chemistry. Studying not only the total amount of light in these transitions but also their high-resolution spectral shape is key. It yield valuable information about the physical processes setting the accretion, as we assessed with simplified models. We will combine the output of our existing 2.5D and upcoming 3D simulations with published complex models of the line emission. This catalog of predictions will be useful to interpret high-resolution data from instruments recently built or at an advanced phase, revealing for instance whether young accretors need magnetic fields to accrete. We will also use these predictions on James Webb Space Telescope data as part of a larger team. All in all, this project is a low-risk, high-gain contribution to the exciting and rapidly-developing field of planet formation, linked to circumplanetary disks and planet-disk interaction. Using cutting-edge methods and improving on existing results, this timely research will connect observers and theoreticians from various countries and deliver quantifiable outputs to advance the field.

• DFG Programme: Research Grants
• International Connection: China
• Cooperation Partner: Yuhiko Aoyama, Ph.D.