The Monoceros Ring is a ring of stars around the Milky Way which is proposed to consist of a stellar stream torn from the Canis Major Dwarf Galaxy as it merges with the Milky Way over the course of billions of years. It is a complex ringlike structure which wraps around our galaxy three times, formed from the long filament of stars pulled from the Canis Major Dwarf Galaxy by tidal forces as it orbits the Milky Way. The ring has a mass of 100 million solar masses and is 200,000 light years long.[1]
The stream of stars was first reported in 2002 by astronomers conducting the Sloan Digital Sky Survey. It was in the course of investigating this ring of stars, and a closely spaced group of globular clusters similar to those associated with the Sagittarius Dwarf Elliptical Galaxy, that the Canis Major Dwarf Galaxy was discovered. In 2006, a study using 2MASS data cast doubts on the nature of the "Ring", arguing that the data suggests that the ring is actually part of the warped galactic disc of the Milky Way. However, observations using the Anglo-Australian Telescope published in 2007 suggest that a warped disc cannot create the observed structure, which must therefore be formed either by a flare of the Galactic disc or have an extra-Galactic origin.
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