Effect of Deceleration on the Gravitational Instability of Shocked Gas Layers : Astrophysics and Relativity

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We have performed two-dimensional hydrodynamic calculations to investigate effect of deceleration on the gravitational instability of isothermal shocked gas layers. We give the time evolution of the decelerating shocked layer with the corrugation-type perturbation. Our numerical results show that the density perturbation is produced by the tangential flows caused by the corrugated shock front and by the effective gravity due to the deceleration and the gas pressure. The growth rate of the density perturbation and the evolution of the perturbation depend on the initial wavelength of the corrugation-type perturbation. We find that there is the most unstable wave number. In this case, the density perturbation grows well due to the decelerating shock instability in t_<cr>, where it is the time that the self-gravity of the layer becomes equal to the deceleration of the layer. After t_<cr>, the density perturbation continues to grow fast due to the gravitational instability. In this way, the deceleration accelerates the gravitational instability. The gravitational collapse occurs in a half of the free fall time t_<ff> of the preshock gas. On the other hand, if the density perturbation does not grow enough in t_<cr>, the gravitational collapse occurs in t_<ff> or the gravitational collapse does not occur. We discuss the condition of the fast gravitational collapse. Our numerical results suggest that the deceleration of the dense layer in the molecular clouds formed by the H _<II> regions accelerates the formation of the cores, which are observed in molecular clouds beside H _<II> regions.
理論物理学刊行会の論文
1992-08-25

Effect of Deceleration on the Gravitational Instability of Shocked Gas Layers : Astrophysics and Relativity

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