Local gravitational stability of a gas disk
For a razor-thin rotating ideal fluid disk, local axisymmetric tightly wound perturbations have dispersion ω²=κ²−2πGΣ|k|+c_s²k².
Key knowledge
For a razor-thin rotating ideal fluid disk, local axisymmetric tightly wound perturbations have dispersion ω²=κ²−2πGΣ|k|+c_s²k². Rotation and pressure oppose self-gravity. The model is stable against every such local wavelength if Q_g=c_sκ/(πGΣ)>1; equality is the marginal case.
Values and equations
ω²=κ²−2πGΣ|k|+c_s²k²; Q_g=c_sκ/(πGΣ)
- ω,κ
- perturbation and epicyclic angular frequencies s⁻¹
- k
- radial perturbation wavenumber m⁻¹
- Σ
- unperturbed surface mass density kg m⁻²
- c_s
- linearized gas sound speed m s⁻¹
- Q_g
- local gas-disk stability parameter 1
- G
- gravitational constant m³ kg⁻¹ s⁻²
Conditions and scope
- Small perturbations, locally uniform background, positive surface density and sound speed,κ²>0, thin-disk potential and axisymmetric tight-winding approximation.
- The gas criterion does not by itself predict star formation or guarantee stability to nonaxisymmetric, multicomponent, magnetic or finite-thickness disturbances. Collisionless stellar disks have a different response.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read the actual Euler/continuity, sound-speed linearization, fluid dispersion and discriminant/Q_g body. Independently minimized the quadratic in |k|; retained strictly local axisymmetric scope, not the full collisionless/nonaxisymmetric chapter.
2026-10-10 · Independent AI editorial review: All44 exact root-authored compact records, equations/variable units/conditions and140 origin edges accepted after independently reading final6/18 with bounded primary bodies and matching prior38/122 scientific fingerprints unchanged. Exact claim/edge review is distinct from combined inventory scope and separate CLE26 approval; no entire cited books or old-corpus experimental revalidation is asserted. Receipt: cosmos-completion-independent-content-and-inventory-review.1.
Entry details
Permanent link to this entry ↗- Record identity
- uni-cosmos-fluid-disk-gravitational-stability
- Revision
- core.1
- Structured reference record
- University core expansion