Point-mass deflection and Einstein angular radius
A point mass in the weak-field geometric-optics limit deflects light by magnitude α̂=4GM/(c²b).
Key knowledge
A point mass in the weak-field geometric-optics limit deflects light by magnitude α̂=4GM/(c²b). For a single thin lens, θ_E²=4GMD_ls/(c²D_lD_s). An ideal point source in perfect source–lens alignment produces a ring with this angular radius in the bounded point-mass model; interpreting observed images requires a lens and distance model.
Values and equations
α̂=4GM/(c²b); θ_E²=4GMD_ls/(c²D_lD_s)
- α̂,θ_E
- physical deflection and Einstein angular radius rad
- M
- point-lens mass kg
- G
- gravitational constant m³ kg⁻¹ s⁻²
- c
- vacuum light speed m s⁻¹
- b
- physical impact parameter m
- D_l,D_s,D_ls
- observer–lens, observer–source and lens–source angular-diameter distances m
Conditions and scope
- M>0, impact parameter b≫2GM/c²; small angles, one isolated lens plane, positive angular-diameter distances and a source behind the lens. Cosmological D_ls is not generally D_s−D_l.
- Extended/asymmetric masses, external convergence/shear and wave or strong-field effects require adaptations; the formula alone identifies neither dark-matter particles nor a unique general mass distribution.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read actual printed pp84–86 deflection integral, point-mass result, distance geometry and Einstein radius. Excluded the dimensionally incomplete mass sentence after64; no all-profile precision claim adopted.
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-point-mass-lens
- Revision
- core.1
- Structured reference record
- University core expansion