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)×104 or 3×104 solar masses.
- Schuster M.T.; et al. (2009). "Imaging the cool hypergiant NML Cygni's dusty circumstellar envelope with adaptive optics". The Astrophysical Journal. 699 (2): 1423–1432. arXiv:0904.4690. Bibcode:2009ApJ...699.1423S. doi:10.1088/0004-637X/699/2/1423.
- Rygl K.; et al. (2012). "Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex. I. Membership of the Cygnus X region". Astronomy and Astrophysics. 539: A79. arXiv:1111.7023. Bibcode:2012A&A...539A..79R. doi:10.1051/0004-6361/201118211.
- Wright N.J.; et al. (2010). "The massive sar-frming rgion Cygnus OB2. II. Integrated sellar poperties and the sar frmation hstory". The Astrophysical Journal. 713 (2): 871–882. arXiv:1003.2463. Bibcode:2010ApJ...713..871W. doi:10.1088/0004-637X/713/2/871.