Growth and sedimentation of dust particles in the vicinity of local pressure enhancements in a solar nebula

Abstract

A planet-forming nebula is a dynamic environment whose properties and structure vary with time. At the early stage of planet formation, when small grains coagulate to form larger objects, the dynamics of such an environment and its time-varying structure have considerable effects on that process. Among such structures, regions where the pressure of the gas is locally enhanced are of particular interest. In the vicinity of these regions, the combined effect of gas drag and pressure gradients, which in a nebula with a monotonic pressure gradient creates gas drag-induced migration of solids towards the central star causes solid particles to migrate inward/outward, and accumulate at the location of the pressure-enhanced region. While migrating, solid particles sweep up smaller objects and grow in size. In this paper, the effects of the appearance of pressure-enhanced structures on the growth and sedimentation of micron-sized particles are studied, and the effects of gas drag and pressure gradients on the rate of accumulation of centimetre-sized objects in the regions of local maximum pressure on the midplane are discussed. To portray a more detailed picture of the dynamical influence of such structures on the motions and interactions of particles, comparisons are made with the results of similar studies in a nebula without pressure-enhanced structures, and the cases, in which the changes in the physical properties of the gas and particles will enhance the growth rates of solids, are discussed. A discussion is also presented on the inelastic collision of dust particles and the corrections to the formulae of sticking velocity that currently exist in the literature.