The Cosmic Horseshoe is the nickname given to a gravitationally lensed system of two galaxies in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Leo Leo is the Latin word for lion. It most often refers to: * Leo (constellation), a constellation of stars in the night sky * Leo (astrology), an astrological sign of the zodiac * Leo (given name), a given name in several languages, usually mas ...

. The foreground galaxy lies directly in front in the line of sight to a more distant galaxy. Due to the passage of the light from the background galaxy through the gravity field of the foreground galaxy, the background galaxy's light is lensed by the warped spacetime environment of the foreground galaxy, thus giving the background galaxy a warped appearance. Unlike most lensed galaxies, the shape of the lensed light of this background galaxy appears shaped like a

horseshoe A horseshoe is a product designed to protect a horse hoof from wear. Shoes are attached on the palmar surface (ground side) of the hooves, usually nailed through the insensitive hoof wall that is anatomically akin to the human toenail, altho ...

. The foreground galaxy, LRG 3-757, is found to be extremely massive, with a mass a hundred times that of the Milky Way galaxy. It is notable because it belongs to a rare class of galaxies called luminous red galaxies, which has an extremely luminous infrared emission. The system was discovered in 2007 by an international team of scientists using the comprehensive

Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...

and is greatly studied by the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

References

{{Leo (constellation) Leo (constellation) Gravitational lensing 20070615