A hydrodynamic mechanism stimulating clump formation in protoplanetary disks*

The clumping of circumstellar material is frequently observed in protoplanetary disks. Once a clump is formed, gravity acts to concentrate the mass, possibly leading to the formation of planetesimals and subsequent orbital bodies. The precise mechanisms that stimulate clump formation, however, are not well understood. In this study, we assess the viability of the Crow instability, a hydrodynamic mechanism affecting interacting vortex cores, in stimulating the formation of clumps. Crow-unstable vortex cores may form via the Kelvin-Helmholtz instability induced by the interaction of stellar wind with the protoplanetary disk. Azimuthal perturbations of the core positions grow under the influence of their self- and mutually induced velocity fields, causing symmetric kinks in the cores that result in clumps. Our analysis predicts dominant unstable wavenumbers, expected to set the number of clumps along the cores, consistent with the observed number of clumps along existing protoplanetary disks.