© ESA/Hubble & NASA / Judy Schmidt
This charming part of the universe is called SDSS J0146-0929, a galaxy cluster which features a great variety of spiral and elliptical galaxies presented to us at different angles - some are face-on, some are angled, but all are locked together by the inescapable tug of gravity. But here, gravity does even more than just hold the galaxies together: it bends light in a way that creates a ring-like feature, a so-called Einstein Ring.
Einstein's ring occurs when light coming from a bright source is bent by the gravitational effect of a very large structure or object - in this case, SDSS J0146-0929. The phenomenon is called gravitational lensing and requires that the three participants (the light source, the massive structure, and the observer - which is Earth) be aligned in a straight-line configuration of called a syzygy.
In this sense, an Einstein Ring is a special case of gravitational lensing, caused by the exact alignment of the source, lens, and observer. This results in a symmetry around the lens, causing a ring-like structure. NASA's Karl Hille describes the image:
"In this image, the light from a background galaxy is diverted and distorted around the massive intervening cluster and forced to travel along many different light paths toward Earth, making it seem as though the galaxy is in several places at once."
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