AG Carinae is a star

Star

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 in the constellation

Constellation

In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Carina

Carina (constellation)

Carina is a constellation in the southern sky. Its name is Latin for the keel of a ship, and it was formerly part of the larger constellation of Argo Navis until that constellation was divided in three.-Stars:...

. It is classified as a luminous blue variable

Luminous blue variable

Luminous blue variables, also known as S Doradus variables, are very bright, blue, hypergiant variable stars named after S Doradus, the brightest star of the Large Magellanic Cloud. They exhibit long, slow changes in brightness, punctuated by occasional outbursts in brightness during substantial...

 and is one of the most luminous stars in the Milky Way

Milky Way

The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

. The large distance (20,000 light-year

Light-year

A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...

s) and intervening dust

Interstellar medium

In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...

 mean that the star is not visible to the naked eye; its apparent brightness

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 varies irregularly between 5.7^m and 9.0^m. The star is surrounded by a large planetary nebula

Planetary nebula

A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...

, formed by material expulsed from the star by its powerful stellar wind

Stellar wind

A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.Different types of stars have...

. The star is apparently in a transitional phase between a massive class O

Stellar classification

In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 blue supergiant

Supergiant

Supergiants are among the most massive stars. They occupy the top region of the Hertzsprung-Russell diagram. In the Yerkes spectral classification, supergiants are class Ia or Ib . They typically have bolometric absolute magnitudes between -5 and -12...

 and a Wolf-Rayet star

Wolf-Rayet star

Wolf–Rayet stars are evolved, massive stars , which are losing mass rapidly by means of a very strong stellar wind, with speeds up to 2000 km/s...

.

External links

• 2MASS Atlas Image Gallery: Miscellaneous Objects — includes an infrared
  Infrared
  Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
  
  image of AG Carinae
• http://jumk.de/astronomie/big-stars/ag-carinae.shtml
• Simbad