The Tucana Dwarf galaxy 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 Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Tucana. It was discovered in 1990 by R.J. Lavery of Mount Stromlo Observatory. It is composed of very old stars and is very isolated from other galaxies. Its location on the opposite side of the Milky Way from other

Local Group The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly , and a total mass of the order of . It consists of two collections of galaxies in a " dumbbell" shape; the Milky Way ...

galaxies makes it an important object for study.

Properties

The Tucana Dwarf 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 as systems that are c ...

of type dE5. It contains only old stars, formed in a single

star formation Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...

era around the time the Milky Way's

globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

s formed. It is not experiencing any current star formation, unlike other isolated dwarf galaxies. The Tucana Dwarf does not contain very much neutral

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

gas. It has a

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

of -1.8, a significantly low number. There is no significant spread in metallicity throughout the galaxy. There does not seem to be any substructure to the stellar distribution in the galaxy.

Location

The Tucana Dwarf is located in the constellation Tucana. It is about away, on the opposite side of the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

galaxy to most of the other

galaxies and is therefore important for understanding the kinematics and formation history of the Local Group, as well as the role of environment in determining how dwarf galaxies evolve. It is isolated from other galaxies, and located near the edge of the Local Group, around from the barycentre of the Local Group—the second most remote of all member galaxies after the Sagittarius Dwarf Irregular Galaxy. The Tucana Dwarf galaxy is one of only two dwarf spheroidal galaxies in the Local Group not located near the Milky Way or the

Andromeda Galaxy The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a Galaxy#Isophotal diameter, D25 isop ...

. It is thought to have approached the Andromeda Galaxy about 11 billion years ago, which ejected the galaxy far away to its current position; such galaxies are called "backsplash galaxies".

References

External links

The Tucana Dwarf Galaxy: HST/WFPC2 Imaging of this Isolated Local Group Dwarf Spheroidal
(AAS) * {{DEFAULTSORT:Tucana Dwarf Dwarf galaxies Dwarf elliptical galaxies Local Group Tucana 69519 Astronomical objects discovered in 1990