Editing Stellar association (section)

===OB associations===
Young associations will contain 10–100 massive stars of [[Stellar classification|spectral class]] [[Stellar classification#Class O|O]] and [[Stellar classification#Class B|B]], and are known as ''OB associations''. These are believed to form within the same small volume inside a [[giant molecular cloud]]. Once the surrounding dust and gas is blown away, the remaining stars become unbound and begin to drift apart.<ref name="GAIA">{{cite web
 | date =2000-04-06
 | url = http://www.rssd.esa.int/SA-general/Projects/GAIA_files/LATEX2HTML/node27.html
 | title = OB Associations
 | publisher = The GAIA Study Report: Executive Summary and Science Section
 | access-date = 2006-06-08 }}</ref> It is believed that the majority of all stars in the Milky Way were formed in OB associations.<ref name="GAIA" />

[[Stellar classification#Class O|O class]] stars are short-lived, and will expire as [[supernova]]e after roughly one to fifteen million years, depending on the mass of the star. As a result, OB associations are generally only a few million years in age or less. The O-B stars in the association will have burned all their fuel within
10 million years. (Compare this to the current age of the [[Sun]] at about 5 billion years.)

The [[Hipparcos]] satellite provided measurements that located a dozen OB associations within 650 [[parsec]]s of the Sun.<ref>{{cite journal
 |author1=de Zeeuw, P. T. |author2=Hoogerwerf, R. |author3=de Bruijne, J. H. J. |author4=Brown, A. G. A. |author5=Blaauw, A.
 | title=A HIPPARCOS Census of the Nearby OB Associations
 | journal=The Astronomical Journal | year=1999
 | volume=117 | issue=1 | pages=354–399
 | doi=10.1086/300682 | arxiv=astro-ph/9809227| bibcode=1999AJ....117..354D|s2cid=16098861 }}</ref> The nearest OB association is the [[Scorpius–Centaurus association]], located about 400 [[light-year]]s from the [[Sun]].<ref>{{cite journal
 | last = Maíz-Apellániz  | first = Jesús
 | title=The Origin of the Local Bubble
 | journal=The Astrophysical Journal | year=2001
 | volume=560 | issue = 1
 | pages=L83–L86
 | doi = 10.1086/324016 | arxiv=astro-ph/0108472| bibcode=2001ApJ...560L..83M| s2cid = 119338135
 }}</ref>

OB associations have also been found in the [[Large Magellanic Cloud]] and the [[Andromeda Galaxy]]. These associations can be quite sparse, spanning 1,500 [[light-year]]s in diameter.<ref>{{cite journal
 |author1=Elmegreen, B. |author2=Efremov, Y. N.
 | title=The Formation of Star Clusters
 | journal=American Scientist | year=1999 | volume=86
 | issue=3 | pages=264
 | url=http://www.americanscientist.org/issues/feature/the-formation-of-star-clusters/2
 | access-date=2006-08-23 | doi=10.1511/1998.3.264 | bibcode=1998AmSci..86..264E|s2cid=262334560
 | url-access=subscription}}</ref>