Cygnus OB2

Cygnus OB2 is a large young cluster of stars in the constellation of Cygnus.
The cluster is an OB association. It includes some of the most massive and most luminous stars known. An example is the suspected luminous blue variable Cyg OB2 #12. The cluster also includes one of the largest known stars, NML Cygni.
The region is inside an even larger area of star formation called 'Cygnus X'. This is one of the most luminous objects in the sky at radio wavelengths. The region is about 1,400 parsecs away fron us.
Although it is huge, Cygnus OB2 is hidden behind a massive dust cloud known as the Cygnus Rift. This hides many of the stars. This means that, despite its size, it is hard to see in detail. The estimated number of massive stars range from 50 to 100 of spectral type O. Its total mass is calculated as (4–10) or 3 solar masses.