TheTrifid Nebula (catalogued asMessier 20 orM20 and asNGC 6514) is anH II region in the north-west ofSagittarius in astar-forming region in theMilky Way'sScutum–Centaurus Arm.[4] It was discovered byCharles Messier on June 5, 1764.[5] Its name means 'three-lobe'. The object is an unusual combination of anopen cluster ofstars, anemission nebula (the relatively dense, reddish-pink portion), areflection nebula (the mainlyNNE blue portion), and adark nebula (the apparent 'gaps' in the former that cause the trifurcated appearance, also designatedBarnard 85). Viewed through a smalltelescope, the Trifid Nebula is a bright and peculiar object, and is thus a perennial favorite of amateur astronomers.[6]
The most massive star that has formed in this region is HD 164492A, anO7.5III star with a mass more than 20 times themass of the Sun.[7]This star is surrounded by a cluster of approximately 3100 young stars.[8]
The Trifid Nebula was the subject of an investigation by astronomers using theHubble Space Telescope in 1997, using filters that isolate emission fromhydrogenatoms,ionizedsulfur atoms, and doubly ionizedoxygen atoms. The images were combined into a false-color composite picture to suggest how the nebula might look to the eye.
The close-up images show a dense cloud of dust and gas, which is astellar nursery full of embryonic stars. This cloud is about8 ly away from the nebula's central star. Astellar jet protrudes from the head of the cloud and is about0.75 ly long. The jet's source is a young stellar object deep within the cloud. Jets are the exhaust gasses of star formation and radiation from the nebula's central star makes the jet glow.
The images also showed a finger-like stalk to the right of the jet. It points from the head of the dense cloud directly toward the star that powers the Trifid Nebula. This stalk is a prominent example ofevaporating gaseous globules, or 'EGGs'. The stalk has survived because its tip is a knot of gas that is dense enough to resist being eaten away by the powerful radiation from the star.
The Trifid Nebula. The outlined area is enlarged right.
Hubble image of a stellar jet in the Trifid Nebula
This video sequence compares a new view of the Trifid Nebula in infrared light, from the VVV VISTA survey with a more familiar visible-light view from a small telescope.
The Trifid Nebula
Trifid Nebula close-up
Widefield image of the Trifid Nebula next toLagoon Nebula
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