Abstract
The fragmentation of the dust layer due to the gravitational instability is one of the possible models of the planetesimal formation. In this work, we preformed the numerical simulations of two different models: the one-fluid model in which the difference of the velocities of the dust and the gas are neglected and the two-fluid model in which the dust and the gas are considered individually. In the one-fluid model, the unstable mode of the gravitational instability grows and concave density distributions arise right and left of the density maximum around the midplane. The evolution of the dust layer in the two-fluid model depends on the gas friction time. When the gas friction time is equal to 2.6x10-3 year, the evolution similar to the one-fluid model occurs after the dust particles settle somewhat toward the midplane. On the other hand, if the friction time is equal to 2.9x10-2 year, the dust settling proceeds before the growth of the gravitational instability; it is not clear whether the fragmentation of dust layer occurs before the dust layer becomes thin infinitesimally. This difference resulting from the different values of the friction time would be important for the evolution of the dust layer.
