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The Canis Major Dwarf Galaxy (''CMa Dwarf'') or Canis Major Overdensity (''CMa Overdensity'') is a disputed dwarf irregular galaxy in the Local Group, located in the same part of the sky as the constellation Canis Major. The supposed small galaxy contains a relatively high percentage of red giant stars, and is thought to contain an estimated one billion stars in all. The Canis Major Dwarf Galaxy is classified as an irregular galaxy and is now thought to be the closest neighbouring galaxy to our location in the Milky Way, being located about 25,000 light-years away from our Solar System and 42,000 light-years from the Galactic Center. It has a roughly elliptical shape and is thought to contain as many stars as the Sagittarius Dwarf Elliptical Galaxy, the previous contender for closest galaxy to our location in the Milky Way. ==Discovery== The existence of a strong elliptical-shaped stellar over-density was reported in November 2003 by an international team of French, Italian, British and Australian astronomers, who claimed their study pointed to a newly discovered dwarf galaxy: the Canis Major Dwarf Galaxy.〔(【引用サイトリンク】 A dwarf galaxy remnant in Canis Major: the fossil of an in-plane accretion onto the Milky Way )〕 This structure is located closer to the Sun than the center of our Galaxy, at approximately 7 kpc from the Sun. The team of astronomers that discovered it were collaborating on analysis of data from the Two-Micron All Sky Survey (2MASS), a comprehensive survey of the sky in infrared light, which is not blocked by gas and dust as severely as visible light. Because of this technique, scientists were able to detect a very significant over-density of class M giant stars in a part of the sky occupied by the Canis Major constellation, along with several other related structures composed of this type of star, two of which form broad, faint arcs. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Canis Major Overdensity」の詳細全文を読む スポンサード リンク
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