Editing Canis Major Overdensity (section)

==Characteristics==

Some astronomers believe that the CMa overdensity is a dwarf galaxy in the process of being pulled apart by the [[gravitational field]] of the more massive Milky Way galaxy. The main body of the CMa is extremely degraded. [[Tidal force|Tidal disruption]] causes a filament of stars to trail behind it as it orbits the Milky Way, forming a complex ringlike structure, sometimes referred to as the [[Monoceros Ring]], which wraps around the Milky Way three times,<ref name="Masetti2011">{{Cite web |title=The Nearest Galaxies |url=http://heasarc.nasa.gov/docs/cosmic/nearest_galaxy_info.html |last=Maggie Masetti |date=14 April 2011 |website=The Cosmic Distance Scale |publisher=[[NASA]] |access-date=26 November 2011 |archive-date=26 November 2011 |archive-url=https://web.archive.org/web/20111126202215/http://heasarc.nasa.gov/docs/cosmic/nearest_galaxy_info.html |url-status=dead }} See section "The Canis Major Dwarf".</ref> The stream of stars was discovered in the early 21st century by astronomers conducting the [[Sloan Digital Sky Survey]]. The Monoceros Ring is similar to the [[Virgo Stellar Stream]] which is thought to be the result of the [[Milky Way]] tearing stars and gases from the [[Sagittarius Dwarf Spheroidal Galaxy]] into a Stellar Stream. It was in the course of investigating the Monoceros Ring, and a closely spaced group of [[globular clusters]] similar to those associated with the Sagittarius Dwarf Elliptical Galaxy, that the CMa Overdensity was discovered.

Globular clusters thought to be associated with the CMa include [[NGC 1851]], [[Messier 79|NGC 1904]], [[NGC 2298]] and [[NGC 2808]], all of which may have been part of the galaxy's globular cluster system before [[accretion (astrophysics)|accreting]] into the Milky Way. [[NGC 1261]] is another nearby cluster, but its velocity differs enough to make its relationship to the system unclear. Additionally, Dolidze 25 and [[NGC 2467|H18]] are [[open cluster]]s that may have formed when the dwarf galaxy perturbed material in the [[Disc (galaxy)|galactic disk]], stimulating [[star formation]].<ref name="Martin2003" />

The discovery of the CMa and subsequent analysis of the stars associated with it has provided some support for the current theory that galaxies may grow in size by swallowing their smaller neighbors. Martin et al.<ref name="Martin2003" /> believe that the preponderance of evidence points to the accretion of a small [[satellite galaxy]] of the Milky Way which was orbiting roughly in the plane of the galactic disk.