The Trifid Nebula, cataloged by astronomers as Messier 20 or NGC 6514, is a well-known region of star formation lying within our own Milky Way Galaxy. It is called the Trifid because the nebula is overlain by three bands of obscuring interstellar dust, giving it a trisected appearance as seen in small telescopes. The Trifid lies about 9,000 light-years (2,700 parsecs) from Earth, in the direction of the constellation Sagittarius.
This new image from the Hubble Space Telescope offers a close-up view of the center of the Trifid Nebula, near the intersection of the dust bands, where a group of recently formed, massive, bright stars is easily visible. These stars, which astronomers classify as belonging to the hottest and bluest types of stars called type "O," are releasing a flood of ultraviolet radiation that dramatically influences the structure and evolution of the surrounding nebula. Many astronomers studying nebulae like the Trifid are focusing their research on the ways that waves of star formation move through such regions.
The group of bright O-type stars at the center of the Trifid illuminates a dense pillar of gas and dust, seen to the right of the center of the image, producing a bright rim on the side facing the stars. At the upper left tip of this pillar, there is a complex filamentary structure. This wispy structure has a bluish color because it is made up of glowing oxygen gas that is evaporating into space. Star formation is no longer occurring in the immediate vicinity of the conspicuous group of bright O-type stars, because their intense radiation has blown away the gas and dust from which stars are made.
The Hubble image of the Trifid Nebula has given astronomers insight into the nature of the interaction of gaseous, dusty and stellar material in an area where dust, gas clouds, and new and old stars coexist. The science team, composed of Farhad Yusef-Zadeh (Northwestern U.), John Biretta (STScI), Bob O'Dell (Vanderbilt U.), and Mark Wardle (Macquarie U.), took exposures in filters that transmit light emitted by oxygen, hydrogen, and sulfur ions. The images were taken with the Wide Field Planetary Camera 2 onboard Hubble in mid-summer 2001 and 2002. This image was produced by the Hubble Heritage Team.
Acknowledgment: F. Yusef-Zadeh (Northwestern Univ.)