The Sagittarius Dwarf Irregular Galaxy (SagDIG) is a

dwarf galaxy A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is so ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

of Sagittarius. (SagDIG should not be confused with the

Sagittarius Dwarf Spheroidal Galaxy The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy (Sgr dE or Sag DEG), is an elliptical loop-shaped satellite galaxy of the Milky Way. It contains four globular clusters in ...

, SagDEG, a satellite galaxy of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

discovered decades later in the same constellation.) It lies about 3.4 million

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distance, astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometers (), or 5.88 ...

s away. It was discovered by Cesarsky ''et al.'' on a

photographic plate Photographic plates preceded photographic film as a capture medium in photography, and were still used in some communities up until the late 20th century. The light-sensitive emulsion of silver salts was coated on a glass plate, typically thinn ...

taken for the ESO (B) Atlas on 13 June 1977 using the ESO 1 meter Schmidt telescope. The SagDIG is thought to be the member of the Local Group most remote from the Local Group's

barycenter In astronomy, the barycenter (or barycentre; ) is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit. A barycenter is a dynamical point, not a physical object. It is an important con ...

. It is only slightly outside the zero-velocity surface of the Local Group. SagDIG is a much more luminous galaxy than the Aquarius Dwarf and it has been through a prolonged period of star formation.Momany ''et al.'' 2005. This has resulted in it containing a rich intermediate-age population of stars. Twenty-seven candidate

carbon stars A carbon star (C-type star) is typically an asymptotic giant branch star, a luminous red giant, whose atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monoxide, which consumes mo ...

have been identified inside SagDIG. Analysis shows that the underlying

stellar population During 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926: Baade noticed ...

of SagDIG is metal-poor (at least e/Hnbsp;≤ −1.3). Further, the population is young, with the most likely average age between 4 and 8 billion years for the dominant population.

References

External links

* {{Sky, 19, 29, 59.0, -, 17, 40, 41, 3390000 Dwarf irregular galaxies Irregular galaxies Sagittarius (constellation) Local Group 63287 Astronomical objects discovered in 1977