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| Paper: |
Theories of molecular cloud formation |
| Volume: |
12, The Evolution of the Interstellar Medium |
| Page: |
247 |
| Authors: |
Elmegreen, Bruce G. |
| Abstract: |
The present overview of cloud-formation mechanisms addresses gravitational instability, the Parker instability, and random collisional agglomeration, and emphasizes two models of formation. The history of the random coalescence model and the Parker instability model are detailed, and the strong and weak points are listed as suggested by observational support. The Jeans instability model is also considered, and cloud formation in shells is mentioned. The observations suggest that cloud-formation processes are distinct from molecule-formation processes, and the presence of molecules in clouds depends on the ambient pressure, metallicity, and the radiation field. The time scale, lifetime, and the molecular fractions of the clouds are understood to an extent, but the geometric configuration of the clouds is an area of future research. |
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