When most people hear the word "nebula," Orion — the nebula most prominently featured in the Orion Molecular Cloud — immediately comes to mind. Indeed, it might be the most well known star forming region in the Milky Way Galaxy, but it isn’t the largest, or even (arguably) the most beautiful. That title (at least the largest) goes to the Great Carina nebula, which can be found about 7,500 light-years from Earth in the Carina constellation.
The nebula itself is over four times larger than the Orion nebula, and exponentially brighter. Only it doesn't appear as bright as Orion due to the fact that Carina is much farther away. This brightness comes from a collection of over 14,000 stars, many are high-mass, blue-white stars that burn brilliantly for only a short period of time, before they explode in a beautiful display of light (supernovae).
This image, which was taken by the Chandra X-Ray Observatory, features many of these stars. NASA explains, "Chandra's X-ray vision provides strong evidence that massive stars have self-destructed in this nearby star-forming region. Firstly, there is an observed deficit of bright X-ray sources in the area known as Trumpler 15, suggesting that some of the massive stars in this cluster were already destroyed in supernova explosions. Trumpler 15 is located in the northern part of the image and is one of ten star clusters in the Carina complex.."
Also seen in this wide-field view of Carina are several noteworthy stars and nebulae, which include the Keyhole nebula, the Homunculus nebula and Mystic Mountain. The most notable star is Eta Carinae (the bright star at left, located near the keyhole nebula), which contains the mass of one hundred Suns. In the near future, the star will go supernova, further enriching the area with the raw materials for star formation.
See a larger image here.