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Reference.org
Cygnus OB2-12
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<p>Cygnus OB2 #12 is an extremely luminous blue <a href="/facts/Hypergiant/Q95EmMhT">hypergiant</a> with an absolute <a href="/facts/Bolometric_magnitude/R8RVxkLx">bolometric magnitude</a> (all electromagnetic radiation) of −10.9, among the <a href="/facts/List_of_most_luminous_stars/dm2k7qw1">most luminous stars known</a> in the <a href="/facts/Milky_Way/ulF6lccN">galaxy</a>. This makes the star nearly two million times more luminous than the Sun, although estimates were even higher when the star was first discovered. It is now known to be a binary, with the companion approximately a tenth as bright. A very approximate initial estimate of the orbit gives the total system mass as 120 M☉ and the period as 30 years. </p>