Gravitational mirage

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A gravitational mirage is the visual impression caused by a so-called gravitational lens in space, which may include multiple images, rings, etc. of background light sources. This is analogous to the familiar mirage which can frequently be observed where the air temperature varies strongly with height over the ground (or sea). The rapidly changing refractive index produces inverted images "floating" in the air.

In other words, a Gravitational Lens, also known as Gravitational Mirage Can wrap itself around an entire Galaxy. This lensing effect was generally predicted in some detail by Albert Einstein over 70 years ago. Rings like this are also referred to as Einstein Rings as a tribute for his findings.

As well as that, Gravitational Mirage is often describes as an illusion seen throughout the sky. When a cluster of galaxies, are sitting between the observer and a far away source of light, it provides a strong curvature in space-time. This deflects all light passing by the object, thus distorting the images received by the observer.

This could also be explained as referring to the bending of light due to the presence of matter in the path that light will be taking, this is explained by Einstein's General Theory of Relativity. Through this process there becomes at least two identical images of one object, separated by a gap, hence the name Cosmic Mirage, which refers to the similar process by which mirages on Earth are created.

History

This effect was founded by astronomers in 1919 during a total solar eclipse. Accurate measurements of stars seen in the dark sky near the eclipsed Sun indicated a displacement in the direction opposite to the Sun, about as much as predicted by Einstein's theory. The effect is due to the gravitational attraction of the photons when they pass near the Sun on their way to Earth. This was a direct confirmation of an entirely new phenomenon and it represented a milestone in physics.In the 1930s, astronomer Fritz Zwicky (1898 - 1974), of Swiss nationality and working at the Mount Wilson Observatory in California, realised that the same effect may also happen far out in space where galaxies and large galaxy clusters may be sufficiently compact and massive to bend the light from even more distant objects. It was only five decades later, in 1979, that his ideas were confirmed when the first example of a cosmic mirage was discovered (as two images of the same distant quasar). Cosmic mirages are generally seen as Numerous images of a single quasar, lensed by a galaxy located between the quasar and Earth. The number and the shape of the images of the quasar depends on the positions of the quasar, the lensing galaxy and Earth. If the alignment were perfect, we would also see a ring-shaped image around the lensing object. Such "Einstein rings" are very rare, though, and have only been observed in a very few cases. Another particular interest of the gravitational lensing effect is that it may not only result in double or multiple images of the same object, but also that the brightness of these images increase, just as it happens with an ordinary optical lens. Distant galaxies and galaxy clusters may act as "natural telescopes" which allow us to observe objects further away that would otherwise have been too faint to be located with currently available astronomical telescopes.

References

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