Westerlund 1-26

Westerlund 1-26

-is 2000 Times bigger than the Sun..

Since its discovery, Westerlund 1-26 has been well known as a strong radio source. Its physical properties are not well understood, due to very high interstellar extinction between Earth and the cluster. Its strong radio emission leads to varying estimates of its size. But precise estimates give it the radius within 1,500 solar radii. However, such scales are given, with some taking it larger than 2,500 solar radii.

Westerlund 1-26 is classified as a luminous supergiant, occupying the upper right corner of theHertzsprung-Russell diagram. With its surface temperature of about 3000 K, it is a very cool supergiant, emitting mostly its energy in the infrared spectrum. It also shows huge mass loss of considerable material, suggesting that it may further evolve into a Wolf-Rayet star.

Westerlund 1-26 has been seen as a star that changes its spectral class during several periods, but it has not been seen to change its luminosity, unlike other stars. No one knows why. One possibility is that the dust extinction only passes a particular wavelength in the spectrum, allowing only the color to be seen while the inert brightness is blocked. But if it doesn't change its luminosity, it will be the first discovered variable star of its type.

In October 2013, astronomers using the European Southern Observatory's Very Large Survey Telescope (VST) discovered that Westerlund 1-26 is surrounded by a glowing cloud of ionized hydrogen. This is the first "ionized nebula" to be have been discovered around a red giant star. The nebula extends 1.30 parsecs of the star and contains considerable material with a temperature of 800 K. Oddly enough, the nebula was very similar to the one at Sanduleak -69° 202 before it exploded as SN 1987A.