The Sextans Dwarf Spheroidal is a
dwarf spheroidal galaxy
A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and to systems that are comp ...
that was discovered in 1990 by
Mike Irwin
Mike may refer to:
Animals
* Mike (cat), cat and guardian of the British Museum
* Mike the Headless Chicken, chicken that lived for 18 months after his head had been cut off
* Mike (chimpanzee), a chimpanzee featured in several books and document ...
as the 8th satellite 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 ...
, located in the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
of
Sextans
Sextans is a minor celestial equator, equatorial constellation which was introduced in 1687 by Johannes Hevelius. Its name is Latin for the sextant (astronomical), astronomical sextant, an instrument that Hevelius made frequent use of in his ob ...
. It is also an
elliptical galaxy
An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The R ...
, and displays a
redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in f ...
because it is receding from the Sun at 224 km/s (72 km/s from the Galaxy). The distance to the galaxy is 320,000 light-years and the diameter is 8,400 light-years along its major axis.
Like other dwarf spheroidal galaxies, the Sextans Dwarf's population consists of old,
metal-poor
In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...
stars: one study found that the majority of stars have a metallicity between
e/H= −3.2 and −1.4. An analysis of several stars found them to also be deficient in
barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
, except for one star.
References
{{DEFAULTSORT:Galaxy, Sextans Dwarf Spheroidal
Dwarf spheroidal galaxies
Local Group
Milky Way Subgroup
Sextans (constellation)
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