2002/07/25 by S. Fromang, Sebastien Fromang, Steven A. Balbus +2
Computer Science · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics (astro-ph) #Computational Physics and Python Applications #Experimental and Theoretical Physics Studies #FOS: Physical sciences #Geophysics and Gravity Measurements #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0207561
8 pages, AAS Tex Macros, Submitted to ApJ (Letters)
arxiv created 2002/07/25 · openalex publication_date 2002/07/25 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
A simple variational calculation is presented showing that a uniformly rotating barotropic fluid in an external potential attains a true energy minimum if and only if the rotation profile is everywhere subsonic. If regions of supersonic rotation are present, fluid variations exist that could take the sytem to states of lower energy. In any given system, these states may or may not be dynamically accessible, but their existence is important. It means that extending the degrees of freedom available to the fluid (say by weak magnetic fields) may open a path to fluid instabilities. Whether astrophysical gaseous nebula tend toward states of uniform rotation or toward more Keplerian core-disk systems appears to be largely a matter of whether the rotation profile is transonic or not. The suggestion is made that the length scale associated with coherent molecular cloud cores is related to the requirement that the cores be stable and rotate subsonically.