Westerlund 1-20 (abbreviated to Wd 1-20 or just W20) is a
red supergiant (RSG) located in the
Westerlund 1
Westerlund 1 (abbreviated Wd1, sometimes called Ara Cluster) is a compact young super star cluster about 3.8 kpc (12,000 ly) away from Earth. It is thought to be the most massive young star cluster in the Milky Way, and was discovered by Ben ...
super star cluster
A super star cluster (SSC) is a very massive young open cluster that is thought to be the precursor of a globular cluster. These clusters called "super" because they are relatively more luminous and contain more mass than other young star clusters. ...
. Its radius was calculated to be around 965
solar radii (6.72 × 10
8 km, 4.48
au), making it one of the
largest stars discovered so far. This corresponds to a volume 899 million times bigger than the
Sun. If placed at the center of the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
, the
photosphere
The photosphere is a star's outer shell from which light is radiated.
The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
of Westerlund 1-20 would almost reach the orbit of
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
.
The star is classified as a luminous cool
supergiant emitting most of its energy in the
infrared spectrum
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
. W20 occupies the upper right corner of the
Hertzsprung-Russell diagram. Using the effective temperature of 3,500 K,
the
bolometric luminosity of 126,000
L☉ and the solar effective temperature of 5,772 K, its radius can be calculated using the
Stefan-Boltzmann law.
Westerlund 1-20 was observed to have an extended, cometary shaped nebula, similar to the other red supergiant
Westerlund 1 W26
Westerlund 1 W26 (commonly abbreviated to W26) or Westerlund 1 BKS AS is a red supergiant located at the outskirts of the Westerlund 1 super star cluster. It is one of the largest known stars and the most luminous supergiant stars dis ...
. It is therefore likely that its morphology was affected by either the
intracluster medium or the cluster wind of Westerlund 1. The nebulae of both Westerlund 1-20 and Westerlund 1 W26 are extended outward from the cluster core and most bright at inward direction, indicating the outward cluster wind.
See also
*
Westerlund 1-237
Westerlund 1-237 or Wd 1-237 is a possible red supergiant (RSG) in the constellation of Ara. It is one out of 4 known red supergiants in the Westerlund 1 super star cluster, although its outlying position, spectrum, and parallax, sugges ...
*
Westerlund 1-75
Westerlund 1 W75 or Wd 1-75 is a red supergiant (RSG) located in the Westerlund 1 super star cluster. Its radius is calculated to be around 668 solar radii (4.65 × 108 km, 3.10 au). This corresponds to a volume 298 million times big ...
*
List of largest known stars
Below are lists of the largest stars currently known, ordered by radius and separated into categories by galaxy. The unit of measurement used is the radius of the Sun (approximately ).
The angular diameters of stars can be measured directly us ...
Notes
References
{{DEFAULTSORT:Westerlund 1-20
Ara (constellation)
M-type supergiants
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