Roche geometry and binary mass transfer
In a circular two-point-mass binary's corotating frame, the effective potential per mass is Φ_eff=−GM₁/r₁−GM₂/r₂−Ω²(x²+y²)/2, with origin at the barycentre and Ω²=G(M₁+M₂)/a³.
Key knowledge
In a circular two-point-mass binary's corotating frame, the effective potential per mass is Φ_eff=−GM₁/r₁−GM₂/r₂−Ω²(x²+y²)/2, with origin at the barycentre and Ω²=G(M₁+M₂)/a³. Its equipotentials approximate the shape of a synchronized hydrostatic donor. Filling the donor's critical Roche lobe permits flow toward the companion through the inner neck; companion winds provide another supply route. Transfer changes mass and angular momentum, so isolated-star evolution can fail.
Values and equations
Φ_eff=−GM₁/r₁−GM₂/r₂−Ω²(x²+y²)/2; Ω²=G(M₁+M₂)/a³
- Φ_eff
- effective potential per unit test mass m² s⁻²
- M₁,M₂
- binary component masses kg
- r₁,r₂,x,y,a
- component distances, corotating barycentric coordinates and separation m
- Ω
- circular orbital angular frequency s⁻¹
- G
- gravitational constant m³ kg⁻¹ s⁻²
Conditions and scope
- Point-mass gravitational approximation, circular orbit, synchronous quasi-hydrostatic donor and separation a>0; r₁,r₂ are distances from the two mass centres. Moving gas also experiences Coriolis effects, so −∇Φ_eff alone is not its full trajectory equation.
- Roche lobe is distinct from a tidal-disruption/Roche-limit distance. Eccentric/asynchronous systems, pressure, feedback and gas dynamics require fuller models; no universal stable-transfer rate or inevitable explosion follows from lobe filling.
Sources · 3
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- The Roche Potential, handwritten pp.1–4: rotating-frame potential and equipotential stellar shapesSaul Rappaport — MIT8.282JReference guide · PDF
- Stars, actual binary-evolution answer: Roche filling and material transferCole Miller — University of MarylandReference guide
- Astronomy2e23.5, actual mass transfer and wind discussionAndrew Fraknoi, David Morrison and Sidney C. Wolff — OpenStaxReference guide
Evidence and review
Visually read original MIT scanned pp.1–4 (PDF text extraction was empty): coordinate/centrifugal-potential derivation and equipotential-shape description; also read Miller's actual lobe-filling transfer answer and OpenStax binary/wind body. Critical-neck language is the stated geometrical interpretation of the effective potential. Excluded the notes' all-five-Lagrange-points-maxima wording and unsupported full trajectory or mass-transfer stability claims.
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.
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