Journal Article

On lensing by a cosmological constant

Fergus Simpson, John A. Peacock and Alan F. Heavens

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 3, pages 2009-2016
Published in print March 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.16032.x
On lensing by a cosmological constant

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Several recent papers have suggested that the cosmological constant Λ directly influences the gravitational deflection of light. We place this problem in a cosmological context, deriving an expression for the linear potentials which control the cosmological bending of light, finding that it has no explicit dependence on the cosmological constant. To explore the physical origins of the apparent Λ-dependent potential that appears in the static Kottler metric, we highlight the two classical effects which lead to the aberration of light. The first relates to the observer's motion relative to the source, and encapsulates the familiar concept of angular diameter distance. The second term, which has proved to be the source of debate, arises from cosmic acceleration, but is rarely considered since it vanishes for photons with radial motion. This apparent form of light bending gives the appearance of curved geodesics even within a flat and homogeneous universe. However, this cannot be construed as a real lensing effect, since its value depends on the observer's frame of reference. Our conclusion is thus that standard results for gravitational lensing in a universe containing Λ do not require modification, with any influence of Λ being restricted to negligible high-order terms.

Keywords: gravitational lensing; cosmology: theory

Journal Article.  5069 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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