M17 Omega Nebula

The Omega Nebula (also known as the Swan Nebula, M17 and NGC 6618) is an HII region in the constellation Sagittarius. It was discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764.
The Omega Nebula is located at a distance between 5000 and 6000 light years, and has a size of about 15 light years in diameter, being associated with a molecular cloud about 40 light years in diameter and a mass of 30000 solar masses.

The total mass of the Omega Nebula is estimated at about 800 solar masses and is one of the brightest and most massive HII regions in our galaxy; if it does not appear more impressive, it is because it looks practically “singing”.

There is a cluster (NGC 6618) in the nebula, which contains at its center two stars of spectral type O4V, and also two stars of type O5V, and 100 stars of spectral type earlier than B9. It is the radiation from these hot, young stars—especially the two O4Vs—that excites and makes the nebula’s gases glow; Recent studies show that this is one of the youngest known clusters, with an age that does not reach even one million years and that the nebula surely houses between 8000 and 10000 stars that have been born in it, 1/3 of them in the cluster NGC 6618.