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An embedded lens is a gravitational lens such that the mass of the lens is a part of the mean mass density of the background universe and not simply superimposed upon it as is done in the standard gravitational lensing theory.〔Peter Schneider, Jürgen Ehlers and Emilio E. Falco, 1992, ''Gravitational Lenses'', (Springer-Verlag, Berlin)〕 For a homogeneous background Universe, a spherical sphere is removed and a lens of mass equal to the removed dust sphere is placed at the center of the void. The mass condensation can be either a point mass or distributed mass, but should be spherically symmetric with respect to the center of the void. If the background universe also contains a non-vanishing cosmological constant Λ, then Λ is required to be the same inside and outside of the void. The metric describing the geometry within the void can be Schwarzschild or Kottler〔F., Kottler, 1918, Annals of Physics (Leipzig), 361, 401〕 depending on whether there is a non-zero cosmological constant. Embedding a lens effectively reduces the gravitational potential's range, i.e., partially shields the lensing potential produced by the lens mass condensation. For example, a light ray grazing the boundary of a Kottler/Schwarzschild void will not be bended by the lens mass condensation (i.e., does not feel the gravitational potential of the embedded lens) and travels along a straight line path in a flat background universe. == Properties == In order to be an analytical solution of the Einstein's field equation, the embedded lens has to satisfy the following conditions: # The mass of the embedded lens (point mass or distributed), should be the same as that from the removed sphere. # The mass distribution within the void should be spherically symmetric. # The cosmological constant should be the same inside and outside of the embedded lens. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Embedded lens」の詳細全文を読む スポンサード リンク
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