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Chapter 5. Collapse and Fragmentation of Isothermal Clouds

1988; Oxford University Press; Volume: 96; Linguagem: Inglês

10.1143/ptps.96.63

0375-9687

Shinji Narita, Shoken M. Miyama, Masayoshi Kiguchi, Chûshirô Hayashi,

Planetary Science and Exploration

We review and summarize the features of collapse and fragmentation of isothermal interstellar clouds. When a cloud collapses by its self-gravity, fragmentation occurs at a stage which is early or late, depending on the cloud mass. Fragmentation occurs at an early stage of collapse if a cloud is massive compared with the initial Jeans mass. On the other hand, a small cloud does not fragment at least until the central core becomes opaque and ceases to be collapsing. A sheet-like or a filamentary cloud is likely to fragment. The typical size of a fragment is several times the thickness of a sheet or the radius of a filament. Most fragments of a sheet are elongated, and massive enough to collapse if the external pressure is negligible. Accordingly they collapse and become filamentary. After a filament becomes opaque and stops collapsing, it fragments to form blobs with small masses of the order of 10-1M⊙-10-3M⊙. If there is some rotation, a collapsing cloud forms not filaments but spiral arms. It is possible that the central part of these spiral arms eventually fragments to blobs with the masses of the order of 10-1M⊙-10-3M⊙.