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Giant Molecular Cloud - formed Behind the visible part of...

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Giant Molecular Cloud The nebula is lit up by the fluorescence of the hydrogen gas around a O-type star in the Trapezium cluster of four stars at the heart of the nebula. The O-type star is so hot that it produces a large amount of ultraviolet light. The ultraviolet light ionizes the surrounding hydrogen gas. When the electrons recombine with the hydrogen nuclei, they produce visible light. Several still-forming stars are seen close to the Trapezium stars. They appear as oblong blobs in the figure below with their long axis pointed toward the hot Trapezium stars. If you select the image, an expanded view of the Trapezium cluster will appear in another window. Both images are from the Hubble Space Telescope (courtesy of Space Telescope Science Institute ).
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H II regions mark sites of star formation because they are formed by hot, young stars. Recall from the table at the beginning of the chapter that O-type stars live just a few million years, a very short time for a star! They do not live long enough to move out from where they were
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Unformatted text preview: formed. Behind the visible part of the Orion Nebula is a much denser region of gas and dust that is cool enough for molecules to form. Several hundred stars are now forming inside the Orion Nebula. Fragments of giant molecular clouds with tens to hundreds of solar masses of material a piece will start collapsing for some reason all at about the same time. Possible trigger mechanisms could be a shock wave from the explosion of a nearby massive star at its death or from the passage of the cloud through regions of more intense gravity as found in the spiral arms of spiral galaxies. These shock waves compress the gas clouds enough for them to gravitationally collapse. Gas clouds may start to collapse without any outside force if they are cool enough and massive enough to spontaneously collapse. Whatever the reason, the result is the same: gas clumps compress to become protostars....
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Giant Molecular Cloud - formed Behind the visible part of...

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