Polytropic stellar structure and Lane–Emden equation
A spherical Newtonian hydrostatic polytrope assumes P=Kρ¹⁺¹⁄ⁿ.
Key knowledge
A spherical Newtonian hydrostatic polytrope assumes P=Kρ¹⁺¹⁄ⁿ. Writing ρ=ρ_cθⁿ and r=bξ reduces mass and pressure balance to ξ⁻²d(ξ²θ′)/dξ=−θⁿ, with regular central conditions θ(0)=1 and θ′(0)=0. Its first zero, when finite, defines the model surface.
Values and equations
(1/ξ²)d(ξ²dθ/dξ)/dξ=−θⁿ; b²=(n+1)Kρ_c^(1/n−1)/(4πG)
- ξ,θ,n
- dimensionless radius, density function and polytropic index 1
- b
- radial scaling length m
- ρ_c
- central mass density kg m⁻³
- K
- constant in P=Kρ^(1+1/n) Pa (kg m⁻³)^(−1−1/n)
- G
- gravitational constant m³ kg⁻¹ s⁻²
Conditions and scope
- K>0,ρ_c>0,n>0; b²=(n+1)Kρ_c¹⁄ⁿ⁻¹/(4πG). Use the positive-density portion of a regular solution.
- A polytropic closure does not solve the full luminosity/composition evolution. It need not equal the local adiabatic exponent of a real star.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read polytropic closure, hydrostatic reduction, scale316 and boundary conditions. Excluded claims of only three analytic forms or a universal finite-mass cutoff, which are unnecessary for this reference method.
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-stellar-polytrope
- Revision
- core.1
- Structured reference record
- University core expansion