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 ...

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 ...

Tucana Tucana (The Toucan) is a constellation of stars in the southern sky, named after the toucan, a South American bird. It is one of twelve constellations conceived in the late sixteenth century by Petrus Plancius from the observations of Pieter D ...

. It was discovered in 1990 by R.J. Lavery of

Mount Stromlo Observatory Mount Stromlo Observatory located just outside Canberra, Australia, is part of the Research School of Astronomy and Astrophysics at the Australian National University (ANU). History The observatory was established in 1924 as The Commonwea ...

. 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. 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 and its satellites form ...

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 to systems that are com ...

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 The "medium" is present further soon.-->interstellar space

era around the time the Milky Way's

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

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 the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

gas. It has a

metallicity 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 ...

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 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 ...

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 Sagittarius Dwarf Irregular Galaxy (SagDIG) is a dwarf galaxy in the constellation of Sagittarius. (SagDIG should not be confused with the Sagittarius Dwarf Spheroidal Galaxy, SagDEG, a satellite galaxy of the Milky Way discovered decades ...

. 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 (IPA: ), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy with the diameter of about approximately from Earth and the nearest large galaxy to the Milky Way. The gala ...

. It is therefore likely to have evolved in isolation for most of its history.

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 (constellation) 69519 Astronomical objects discovered in 1990