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Light Deflection
Joachim Wambsganss
Dept. of Astrophysical Sciences - Princeton University

Microlensing pattern indicating the magnification of a distant “quasar” as a function of its position; produced by the light deflection of many stars in an intervening galaxy. 
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According to Einstein’s Theory of Gravity, a ray of light is attracted by a clump of matter. As a consequence of “gravitational lensing”, the light ray changes its direction from a straight line by a minute amount when it passes close to a cosmic object.

Stars and planets in our Milky Way or in other galaxies can thus act as “microlenses”: They focus the light of a background source in a very characteristic way. The main effect is a time-variable magnification of the background source due to relative motion.

In our research, we simulate the effects of light deflection by tracing light rays backward through a field of lensing objects and calculating their deflection.

The colors in the resulting two-dimensional maps in the “source plane” reflect the density of light rays; they indicate the magnification of the background source as a function of its position.

The sharp “caustic lines” are locations of very high magnification. When a background star moves across such a pattern, we can measure its variable brightness with our telescopes and deduce properties of dark matter or discover extrasolar planets.

(via Art of Science)

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