The Omega Nebula (also Swan Nebula, M17,  NGC 6618) was discovered in 1745 by the Swiss astronomer De Cheseaux and is 6.750 lightyears away in the constellation Sagittarius. This is a very young and active star-formation region embedded in a cloud of molecular hydrogen. 
In the center is the 60 M☉ star system "Kleinmann's Anonymus Star", with two O4 V stars that each have another O-type companion. This cluster is approximately 0.5 Myrs old and has nearly 10.000 members. It is the second-brightest H-II region in our galaxy.