The Omega Nebula, also known as the Swan Nebula, catalogued as Messier 17, is an H II region in the rich starfields of the Sagittarius area of the Milky Way (located in the northeast corner of the map on the Sagittarius/Serpens Cauda border). It was discovered by Philippe Loys de Chéseaux in 1745. Charles Messier catalogued it in 1764. The Omega Nebula is between 5,000 and 6,000 light-years from Earth and it spans some 15 light-years in diameter. The total mass of the Omega Nebula is an estimated 800 solar masses.
It is considered one of the brightest and most massive star-forming regions of our galaxy. An open cluster of 35 stars lies embedded in the nebulosity and causes the gases of the nebula to shine due to radiation from these hot, young stars; however, the actual number of stars in the nebula is much higher – up to 800; 100 of spectral type earlier than B9, and 9 of spectral type O, plus >1000 stars in formation on its outer regions. The luminous blue variable HD 168607, located in the south-east part of the Omega nebula, is generally assumed to be associated with it; its close neighbor, the blue hypergiant HD 168625, may be too.
The wave-like patterns of gas have been sculpted and illuminated by a torrent of ultraviolet radiation from young, massive stars, which lie outside the picture to the upper left. The glow of these patterns accentuates the three-dimensional structure of the gases. The ultraviolet radiation is carving and heating the surfaces of cold hydrogen gas clouds. The warmed surfaces glow orange and red in
this photograph. The intense heat and pressure cause some material to stream away from those surfaces, creating the glowing veil of even hotter greenish gas that masks background structures. The pressure on the tips of the waves may trigger new star formation within them. The image, roughly 3 light-years across, was taken May 29-30 1999 taken by NASA’s Hubble Space Telescope, with the Wide Field Planetary Camera 2. The colors in the image represent various gases. Red represents sulfur; green, hydrogen; and blue, oxygen.
Credits: ESO, NASA, Wikipedia.