Formation of giant cloud complexes by the Parker-Jeans instability
The Parker-Jeans instability is considered as a possible mechanism for forming the giant cloud complexes observed near OB associations. We use a previously derived dispersion relation to evaluate the masses and growth times of the dominant modes in this instability. The results show that massive clouds (Mroughly-equal10/sup 6/ M/sub sun/) can form quickly (roughly-equal12 million yr) in the high density environments (5 cm/sup -3/) associated with spiral density wave shocks. For densities larger than about 3 cm/sup -3/, these clouds form primarily as a result of the self-graviational forces in the interstellar medium. Lower mass clouds (Mroughly-equal10/sup 5/ M/sub sun/) can form in lower density environments as a result of the pure Parker instability. The masses of the clouds that form when the density exceeds about 3 cm /sup -3/ are insensitive to the magnetic field strength, cosmic ray pressure, and ambient density (even in compressed media.). These masses are essentially the Jeans mass in a magnetic interstellar medium. The occurrence of a characteristic mass may explain the similarity of the local OB associations. The role of the Parker-Jeans instability as part of a complete theory of cloud formation is summarized.
- Research Organization:
- Department of Astronomy, Columbia University
- OSTI ID:
- 5022859
- Journal Information:
- Astrophys. J.; (United States), Vol. 253:2
- Country of Publication:
- United States
- Language:
- English
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