Dust-gas dynamics driven by the streaming instability with various pressure gradients

The radial pressure gradient (RPG) along the midplane of gaseous protoplanetary disks — planetary nurseries — poses a severe obstacle to planet formation. Micron-sized dust grains, embedded in the disk, must quickly grow to kilometer-sized planetesimals — the building blocks of planets — before fatally drifting inwards, by RPG-induced gas drag, into a central host star. However, the RPG simultaneously powers one of the most robust processes to overcome this radial-drift barrier: the streaming instability (SI). Spontaneously triggered, the SI aerodynamically concentrates drifting dust via drag-induced, coupled interactions and feedback with the surrounding gas. In particular, the nonlinear phase of the SI has not been rigorously or thoroughly studied in the presence of different RPGs, despite implications and expectations from linear analysis. Thus, we numerically simulated and analyzed the nonlinear evolution of the SI among various RPGs in unstratified, 2D shearing sheets, corotating with the disk, using the Athena++ code, extended to include Lagrangian particles with feedback to the gas. Depending on particle size and initial dust concentration, we find that different RPGs noticeably affect the nonlinear growth, saturation, structure, and resultant dust density distributions of the SI, the details of which are not obvious nor expected from linear analysis. Our results offer many new, valuable insights into the complexity of dust-gas dynamics as well as implications for both planet formation theories and protoplanetary disk observations.