DR 21 is a large molecular cloud[1] located in the constellation Cygnus, discovered in 1966 as a radio continuum source by Downes and Rinehart.[2] DR 21 is located about 6,000 light-years (1,800 pc) from Earth and extends for 80 light-years (25 pc).[3] The region contains a high rate of star formation and is associated with the Cygnus X star forming region. It has an estimated mass of 1,000,000 M☉.[4]
An estimated population of 2,900 stars have been formed in this molecular cloud, similar to the population of the Orion Nebula cluster, which are distributed in groups associated with cloud clumps.[7] Feedback from the massive stars may ultimately disrupt the cloud, however this has not yet happened due to the region's extreme youth. Study of these stars by the Spitzer Space Telescope has shown signs of protoplanetary disks.[8]
^Wilson, T. L.; Mauersberger, R. (November 1990). "The Internal Structure of Molecular Clouds. I. C18O, C34S and NH3 Maps of the DR 21/W 75 S Region". Astronomy and Astrophysics. 239 (1–2): 305–318. Bibcode:1990A&A...239..305W.
^Lai, Shih-Ping; Girart, José M.; Crutcher, Richard M. (November 2003). "Interferometric Mapping of Magnetic Fields in Star-forming Regions. III. Dust and CO Polarization in DR 21(OH)". The Astrophysical Journal. 598 (1): 392–399. arXiv:astro-ph/0308051. Bibcode:2003ApJ...598..392L. doi:10.1086/378769. S2CID14746266.
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