M17 (NGC 6618), also called the Swan Nebula and sometimes the Omega Nebula, is a region of new star formation.  This impressive celestial object shines brightly due to excited emissions caused by the high-energy radiation of young stars^[1].  Unlike many other emission nebula, these stars are not obvious in optical images as they are hidden within the nebula^[1].  Star formation is either still active in this nebula, or has ceased very recently^[1].  A small cluster of about 35 bright, but obscured, stars seems to be imbedded in the nebulosity^[1].  The nebula is comprised predominately of hydrogen gas; however, a large component of oxygen is present.  The blue color in the image above comes from this oxygen gas excited to shine by stars lying within the nebula^[1].  The nebula contains a large amount of dark obscuring material comprised of dust and cold gas.  The mass of the gas and dust in the Swan Nebula is estimated to be about 800 times that of the Sun^[2].

While the bright nebula is roughly 15 light years across, the total gaseous cloud, including low-luminosity material, extends to at least 40 light years^[2].  M17 lies in the constellation Sagittarius at an estimated distance of 5,000 to 6,000 light years^[2].

The above image is a mapped, or false, color image and was acquired using narrowband filters.  It was assembled using the standard Hubble Palette with SII mapped to red, Ha mapped to green and OIII mapped to blue.  The stars were overlaid with RGB data to give them a near true color appearance.  A bi-filtered, near true color, image of The Swan Nebula may be viewed here.

References
¹Seds: http://www.messier.seds.org/m/m017.html
²Wikipedia: https://en.wikipedia.org/wiki/Omega_Nebula <