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Einstein Ring

An Einstein ring is the deformation of the light from a source (such as a galaxy or star) into a ring through gravitational deflection of the source's light by a lens (such as another galaxy, or a black hole). This occurs when the source, lens and observer are all aligned.  The bending of light by a gravitational body was predicted by Albert Einstein in 1912, a few years before the publication of General Relativity in 1916. He remarked upon this effect in 1936, but stated, "Of course, there is no hope of observing this phenomenon directly. First, we shall scarcely ever approach closely enough to such a central line. Second, the angle of deflection will defy the resolving power of our instruments." However, Einstein was only considering the chance of observing Einstein rings produced by stars, which is low. But the chance of observing those produced by larger lenses such as galaxies or black holes is higher since the angular size of an Einstein ring increases with the mass of the lens.

Astronomers using NASA's Hubble Space Telescope have compiled a large catalog of gravitational lenses in the distant universe. The catalog contains 67 new gravitationally lensed galaxy images found around massive elliptical and lenticular-shaped galaxies. At least four of the lenses produce Einstein rings, as in the image above, a complete circular image of a background galaxy, which is formed when the background galaxy, a massive, foreground galaxy, and the Hubble Space Telescope are all aligned perfectly.

Hubble astronomers went through a unique process to identify these incredible natural lenses. First, possible galaxies were identified from a galaxy catalog, comprising more than 2 million galaxies. "We then had to look through each individual COSMOS image by eye and identify any potential strong gravitational lenses," said Faure. Finally, checks were made to see if the foreground galaxy and the lensed galaxy were really different or just one galaxy with an odd shape. "With this sample of gravitational systems identified by the human eye, we now plan to use the sample of lenses to train robot software to find more of these lenses across the entire Hubble image archive, and we may find even more strong lensing systems in the COSMOS field," added Kneib.

The new results confirm that the universe is filled with gravitational lensing systems. Extrapolating these new findings to the whole sky predicts no less than half a million similar lenses in total.

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