Canis Major Overdensity

Coordinates: Sky map 07h 12m 35.0s, −27° 40′ 00″
Source: Wikipedia, the free encyclopedia.

Canis Major Overdensity
Observation data (J2000 epoch)
ConstellationCanis Major
Right ascension07h 12m 35.0s[1]
Declination−27° 40′ 00″[1]
Distance25,000 ly
Characteristics
TypeIrr
Number of stars1 billion (1×109)
Apparent size (V)12 degrees × 12 degrees
Other designations
CMa Dwarf,[1] PGC 5065047

The Canis Major Overdensity (CMa Overdensity) or Canis Major Dwarf Galaxy (CMa Dwarf) 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 giants and is thought to contain an estimated one billion stars in all.

At the time of its announcement, the Canis Major Dwarf Galaxy is classified as an irregular galaxy and is thought to be the closest neighboring galaxy to the Earth's location in the

Sagittarius Dwarf Elliptical Galaxy
, the previous contender for closest galaxy to Earth, though later studies disputed this conclusion.

Discovery

The existence of a strong elliptical-shaped stellar overdensity 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.[3] This structure is located closer to the Sun than the center of this galaxy, at approximately 7.7 kpc (25,000 ly) from the Sun.

The team of astronomers that discovered it was 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 overdensity 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.

Characteristics

Some astronomers believe that the CMa overdensity is a dwarf galaxy in the process of being pulled apart by the

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

galactic disk, stimulating star formation.[3]

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.[3] 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.

Dispute

Several studies cast doubts on the true nature of this overdensity.[5] Some research suggests that the trail of stars is actually part of the warped galactic thin disk and thick disk population and not a result of the collision of the Milky Way with a dwarf spheroidal galaxy.[6] Investigation of the area in 2009 yielded only ten RR Lyrae variable stars which is consistent with the Milky Way's halo and thick disk populations rather than a separate dwarf spheroidal galaxy.[7]

In fiction

British science fiction writer Stephen Baxter included the Canis Major Overdensity in his novella "Mayflower II" as the destination of the eponymous starship.

See also

References

  1. ^ a b c "NASA/IPAC Extragalactic Database". Results for Canis Major Dwarf. Retrieved 16 March 2007.
  2. ^ "Astronomers find nearest galaxy to the Milky Way". Archived from the original on 27 May 2008. Retrieved 24 September 2009.
  3. ^
    S2CID 18383992
    .
  4. ^ Maggie Masetti (14 April 2011). "The Nearest Galaxies". The Cosmic Distance Scale. NASA. Archived from the original on 26 November 2011. Retrieved 26 November 2011. See section "The Canis Major Dwarf".
  5. arXiv:1207.2749 [astro-ph.GA
    ].
  6. S2CID 6371010
    .
  7. S2CID 18967866
    .

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Canis_Major_Overdensity&oldid=1192004424"