Boss, Alan Paul | Search NASA

NASA NTRS1982

A Heuristic Criterion for Instability to Fragmentation in Rotating, Interstellar Clouds

A heuristic criterion, based on linear perturbation analysis, is applied to the initial growth of density perturbations in isothermal or adiabatic gas clouds, with initially uniform density and uniform rotation. The heuristic criterion is shown to be consistent with the available results from numerical calculations of cloud collapse. The criterion predicts that perturbations varying as cos (m(phi)) will be most likely to grow when )pi is small, unless the cloud is nearly pressureless.

Boss, Alan Paul↗

NASA NTRS1981

On the Fragmentation of Rotating Interstellar Clouds

Simple physical arguments are used to estimate the time scale for fragmentation of a collapsing, rotating, isothermal, interstellar cloud. This time scale is compared with a similarly estimated time scale for the collapse upon itself of a transitory ring structure. It is shown to be plausible for a cloud with a given ratio of rotational to gravitational energy (beta) that as the ratio of thermal to gravitational energy (alpha) is varied, there is an intermediate range of alpha where a ring forms and collapses on itself, prior to fragmentation. For higher or lower alpha however, the cloud fragments prior to ring self-collapse. The analysis is compared with the results of numerical multidimensional, gravitational, hydrodynamical collapse and shown to be in good agreement with them.

Boss, Alan Paul↗