Physics
Scientific paper
Dec 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984pthph..72.1118n&link_type=abstract
Progress of Theoretical Physics, Vol. 72, No. 6, pp. 1118-1136
Physics
49
Scientific paper
In order to solve the long-standing ``centrifugal bounce or runaway'' problem and also the problem of subsequent dynamical evolution, the collapse of rotating isothermal clouds has been investigated by axisymmetric two-dimensional simulations and also by one-dimensional analysis as well as simulations in a thin disk approximation. For the initial condition, we have considered flattened configurations besides a uniform sphere.The results show that the collapse of the inner region follows a series of similar disk-like configurations nearly independent of initial and boundary conditions: The angular velocity and the column density of the disk are both proportional to ({a_c}(2+tildeω^2)(-1/2)) , and the equatorial density to ({a_c}(2+tildeω^2)(-1)) , where a_c is the core radius decreasing with time and tildeω is the distance from the rotation axis. This similarity law arises from a competition between gravity and pressure in the core, contrary to the previous belief that centrifugal force would play a more significant role than pressure.The above form of column density shows that an axisymmetric disk cloud does undergo runaway collapse as long as it is isothermal, as was found in the simulations of Norman et al. The inner region is not very flattened (its axial ratio or flatness being about 6); hence, it is unlikely that the inner region will be subject to ring formation during the isothermal collapse. However, as for the outer envelope, whether it becomes gravitationally unstable to ring formation depends on its initial condition, i.e., the magnitudes of initial flatness and also density fluctuation.It is also shown that the above mentioned central runaway occurs only when the gas is isothermal. However, the runaway is actually stopped because the core becomes opaque and the gas is no more isothermal. It is found that the departure from isothermality gives rise to a bounce of the core and that, if the cloud is very flattened, it becomes unstable to ring formation, but otherwise it oscillates around an equilibrium state.
Hayashi Chuichiro
Miyama Shoken M.
Narita Shinji
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