Gravitational lensing is the warping of light around objects in space that have a strong gravitational pull like our sun.Einstein general theory of relativity describes how gravity can distort the path of light, altering its trajectory.
Lensing can produce multiple images of a distant source a phenomenon termed strong lensing. The foreground lens is a galaxy and when the background source is a quasar or resolved jet, the strong lensed images are usually point-like multiple images; When the background source is a galaxy or extended jet emission, the strong lensed images can be arcs or rings.
Microlensing ,the temporary brightening of a star due to the magnification induced by a foreground object that crosses the line of sight to the observer. Microlensing has also been effective in the detection of exoplanets as well.
Weak gravitational lensing holds enormous promise in observational cosmology, as the technique, properly employed, can reveal the distribution of dark matter independently of any assumptions about its nature. Dark matter does have mass so we can use gravitational lensing to map the dark matter in the universe.
We can use the effect to peer deeper into the Universe than would otherwise be possible with our conventional telescopes. In fact, the most distant galaxies ever observed, ones seen just a few hundred million years after the Big Bang, were all discovered using gravitational lensing. Astronomers use gravitational microlensing to detect planets around other stars. The foreground star acts as a lens for a background star.
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