Cygnus OB2 is an

OB association In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as t ...

that is home to some of the most massive and most luminous stars known, including suspected

Luminous blue variable Luminous blue variables (LBVs) are massive evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of the Larg ...

Cyg OB2 #12. It also includes one of the largest known stars, NML Cygni. The region is embedded within a wider one of star formation known as Cygnus X, which is one of the most luminous objects in the sky at radio wavelengths. The region is approximately 1,570 parsecs from Earth in the constellation of Cygnus. The young cluster is one of the largest known and the largest in the northern hemisphere with some authors formerly classifying it as a young globular cluster similar to those in the

Large Magellanic Cloud The Large Magellanic Cloud (LMC), or Nubecula Major, is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (≈160,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the ...

. Today, however, it is considered a massive, low-density stellar association. Although it is over ten times more massive than the

Orion Nebula The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the constellation of Orion. It is one of the brightest nebulae and is visible to the naked eye in the nig ...

, which is easily seen with the naked eye, Cygnus OB2 is hidden behind a massive dust cloud known as the Cygnus Rift, which obscures many of the stars in it. This means that despite its large size, it is hard to determine its actual properties. The estimated number of massive stars range from 50 to 100 of spectral type O and its total mass having been calculated as (4–10) or 3

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

es according to other investigations. Despite this, recent surveys ranging from radio to X-ray wavelengths have observed the region to great depths to gain a better understanding of how the processes of star and planet formation occur on such a large scale. These studies include observations with the Chandra X-ray Observatory,

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, f ...

, the

Herschel Space Observatory The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Telesc ...

and the Gran Telescopio Canarias. As for recent observations, the final stages of the process of photoablation is taking place, where the biggest stars formed and cleared the ambient material from the region. The progenitor of

BD+43°3654 BD+43 3654 is a massive luminous blue supergiant runaway star in the constellation Cygnus. Features BD+43 3654 has a spectral type of O4 If with a mass around 65 times larger than the Sun, likely 850,000 times brighter, and very young, w ...

might have been a member of Cygnus OB2. Two stars from two binaries would have collided and merged forming BD+43°3654, which would have then been ejected from the stellar association along with the two remaining stars. Prominent members of the association are often referred to by their Schulte numbers: for example Schulte 12, VI Cygni 12, or Cygnus OB2 #12. The numbers were first used in the 1953 discovery paper where 11 "blue giants" were numbered. A 12th star ( Cyg OB2 #12) was added in 1954, and eight more shortly after. Schulte himself maintained the already-published numbers and added many more when studying the association which he called VI Cygni.

References

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