Einstein Cross

Einstein Cross
Image cropped from an  APOD NASAimage

The rare image of an Einstein Cross taken by professor James Rhoads (Arizona State University) shows a galaxy in unusual light. According to current theory, the large black hole in the centre of the galaxy is hidden from our sight by bright light emitted from a quasar behind the galaxy and on the same axis of view as the black hole. Gravity field is so strong that it bends the tracks of photons creating this amazing cloverleaf of light.


Gravitational lensing

A gravitational lens refers to a distribution of matter (such as a cluster of galaxies) between a distant source (a background galaxy) and an observer, that is capable of bending (lensing) the light from the source, as it travels towards the observer. This effect is known as gravitational lensing and is one of the predictions of Albert Einstein's general theory of relativity.
Although Orest Chwolson is credited as being the first to discuss the effect in print in 1924, the effect is more commonly associated with Einstein, who published a more famous article on the subject in 1936.
Fritz Zwicky posited in 1937 that the effect could allow galaxy clusters to act as gravitational lenses. It was not until 1979 that this effect was confirmed by observation of the so-called "Twin QSO" SBS 0957+561.

Gravitational lens
Image wikimedia

Spacetime around a massive object (such as a galaxy cluster or a black hole) is curved, and as a result light rays from a background source (such as a galaxy) propagating through spacetime are bent. The lensing effect can magnify and distort the image of the background source.

Read the entire article on gravitational lens wikipedia