Westerlund 1 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 discovered so far with radius calculated to be in excess of a thousand times the solar radius, and a luminosity of over 200,000 times the solar luminosity. If placed at the center of the Solar System, its photosphere would engulf the orbit of Jupiter.
Westerlund 1 in infrared from 2MASS
Red supergiants (RSGs) are stars with a supergiant luminosity class and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Antares A are the brightest and best known red supergiants (RSGs), indeed the only first magnitude red supergiant stars.
Betelgeuse pulsating and showing spectral line profile changes (HST UV images)
A red supergiant ends its life as a type II supernova (bottom left) in a spiral arm of M74
RSGC1, the first of several massive clusters found to contain multiple red supergiants.
The Orion region showing the red supergiant Betelgeuse