On the hydrodynamic instability of the two-phase gas-dust layer in the central plane of the fractal protoplanetary disk

One of the key unsolved problems in the theory of the formation of planets is still search for finding an effective mechanism explaining the significant thickening of fine solid particles of a protoplanetary disk into larger dust aggregates, which in turn unite in proto-planetesimal with a large initial mass. Among the mechanisms contributing to the formation of planetesimals, an important place belongs to hydrodynamic instabilities, in particular, the so-called streaming instability of the two-phase gas-dust layer due to its ability to concentrate dispersed particles in dense clots. In the paper, despite the majority of theoretical studies, initially assuming the uniformity of dust particles and their compact structure, it was proposed to extend such an analysis to the case of taking into account the fractal nature and multi-scales of dust aggregates resulting from coagulation. In the framework of this approach, the instability of the dust layer in the central plane of the protoplanetary disk with linear axisymmetric perturbations of its parameters is considered. A preliminary analysis allowed, in particular, to conclude that the presence of dust fractal aggregates of different sizes increases the efficiency of linear growth of the flow instability associated with the difference between the velocities of the dust and gas phases.