The Collapse of Interstellar Gas Clouds--IV Models of Collapse and a Theory of Star Formation

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Abstract
Previously developed numerical methods for the solution of the equations of hydrodynamics with gravitation are applied to a series of cloud models to investigate the roles of heating, cooling and density distribution on the collapse. A characteristic mode of collapse is found for clouds of all masses. This mode of collapse involves the growth of density in the central parts of the gas and in other regions of increased density. In the regions of density growth the velocity field is almost linear wave. The effects of opacity are also investigated and it is shown that the increase of opacity with increasing central density is of critical importance for star formation. The behaviour of small density perturbations is discussed. It is found that small perturbations grow only under certain conditions of the flow, otherwise they will disperse. A discussion of cloud fragmentation is given in which it is shown that fragmentation is a consequence of non-uniform collapse and is enhanced by the interaction of the atomic properties of the interstellar medium with the dynamics of the problem. A theory of stellar evolution—from gas cloud to proto-star—is proposed and justified both in terms of the numerical models presented in this paper and by analytical linear wave flow approximations where appropriate. It is found that the smallest proto-stars which can be formed by this method have a mass ~ 10 32 g. A theory of the formation of interstellar gas clouds is also discussed.

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