Shoken M. Miyama

Gas flow in the solar nebula leading to the formation of Jupiter

Three-dimensional gas flow in the solar nebula, which is subject to the gravity of the Sun and proto-Jupiter, is numerically calculated by using a three-dimensional hydrodynamic code - i.e., the socalled smoothed-particle method. The flow is circulating around the Sun as well as falling into a potential well of proto-Jupiter. The results for various masses of proto-Jupiter show that (1) the e-folding growth time of proto-Jupiter by accretion of the nebular gas is as short as about 300 years in stages where the mass of proto-Jupiter is 0.2 ~ 0.5 times the present Jovian mass, and that (2) proto-Jupiter begins to push away the nebular gas from the orbit of proto-Jupiter and form a gap around the orbit, when its mass is about 0.7 times the present Jovian mass. It is possible that this pushing-away process determined the present Jovian mass.

Three-Dimensional Numerical Simulation of Interstellar Cloud-Cloud Collisions and Triggered Star Formation. I: — Head-On Collisions —

We simulate the head· on collisions between isothermal interstellar clouds by using a three· dimensional hydrodynamic code. The cloud·cloud collision is one of the important mechanisms which trigger star formation. We obtain a new dynamical criterion for the gravitational instability instead of the static criterion for the Bonnor-Ebert sphere, In the collision between identical clouds with relative velocity greater than the sound velocity, the shock compressed layer is formed and the central density increases by the square of the impact Mach number. As a result, the enhanced self-gravity induces the instability and the central part of the cloud begins to collapse even if the total ,

Chapter 8. Efficiency of Angular Momentum Transfer by Shear Instability

In order to calculate the rate of angular momentum transfer by the shear instability, we use perturbation theory. We obtain the lowest order of the flux of the angular momentum, solving the linear order as well as the second order perturbation equations. The differentially rotating cylinder with isentropic and polytropic equation of state is investigated for the sake of simplicity. The angular momentum is found to be transferred effectively near the corotation point where the phase velocity of the unstable mode is equal to the rotation velocity of the cylinder. Using the results we estimate the angular momentum transfer rate in the solar nebula.

Criteria for the collapse and fragmentation of rotating clouds

Three dimensional computations for processes of collapse and fragmentation of rotating gases are performed and criteria for fragmentation of rotating clouds in the cases of the various equation of state are obtained.