Nearly circular galactic disk orbits
In a smooth stationary axisymmetric potential, expanding about a stable circular guiding radius R_g gives small radial oscillations at epicyclic frequency κ and vertical oscillations at ν.
Key knowledge
In a smooth stationary axisymmetric potential, expanding about a stable circular guiding radius R_g gives small radial oscillations at epicyclic frequency κ and vertical oscillations at ν. Their squared values are κ²=R dΩ²/dR+4Ω² and ν²=∂²Φ/∂z², evaluated at the guiding circle and midplane. Angular momentum fixes the guiding radius.
Values and equations
κ²=R dΩ²/dR+4Ω²; ν²=∂²Φ/∂z²; Ω²=(∂Φ/∂R)/R
- κ,ν,Ω
- radial, vertical and circular angular frequencies s⁻¹
- R,z
- cylindrical radius and height m
- Φ
- gravitational potential per unit mass m² s⁻²
Conditions and scope
- Small radial and vertical excursions, symmetric midplane and positive squared frequencies for oscillatory stability; Ω²=(∂Φ/∂R)/R for the circular orbit.
- Bars, spiral perturbations, large excursions and varying vertical density can defeat this local harmonic approximation. No dated Solar-neighborhood frequency or universal rotation-curve range is asserted.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read the effective-potential Taylor expansion and radial/vertical/circular frequency relations. Retained only local conditions; excluded the source's inconsistent epicycle axis-ratio description and present numerical Galactic estimates.
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
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- uni-cosmos-disk-epicyclic-motion
- Revision
- core.1
- Structured reference record
- University core expansion