Star Formation - The Interstellar Medium, The Birth Of A Star, Other Methods Of Star Formation, Current Research On Star Formation
gas cloud contraction cold
Star formation is the process by which a cold, dark cloud of gas and dust is transformed into a brilliant star with a surface temperature anywhere from 3,000-50,000K (4,900–90,000°F; 2,700–50,000°C). Many regions of our galaxy are filled with cold clouds of gas that begin to contract, under certain conditions, as a result of their own gravitational attraction. As one of these clouds contracts, it heats up and tends to become spherical. The heating, however, produces pressure in the gas that counteracts the contraction, and eventually the contraction may stop if the gravity and gas pressure balance one another. If the cloud has become hot enough to begin thermonuclear fusion reactions at its center, it can then sustain itself against its own gravity for a long time. Such a cloud is then called a star.
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When you look up on a clear night, you see stars—thousands of them—glittering against the seemingly empty backdrop of space. But there is something else out there; vast clouds of cold, dark gas and dust, visible only by the dimming effect they have on starlight shining through them. This is the interstellar medium, and it is the birthplace of the stars. In most places the interstella…
Imagine a cloud, drifting along through the interstellar medium. The cloud is unthinkably cold, in excess of -400°F (-240°C). It is not very dense, but it is so large that it renders the stars behind it either invisible or as dim, red points of light. It is made mostly of hydrogen, and has had its present shape and size for thousands of years. Then, one year, something happens. A hun…
The scenario described above leads to a situation like that shown in the Great Orion Nebula. Brilliant, newly born stars blaze in the foreground, while the great cloud surrounding them glows in the background. This nebula glows because the intense radiation from the massive young stars near it is heating it. Contrast this with the Horsehead Nebula, which has no such sources of heat and therefore i…
An important avenue of research involves studying the cycle of star births and deaths in the galaxy. Formation of stars depletes the interstellar medium, since some of its gas goes into making the stars. But then, as a star shines, a small part of its matter escapes its gravity and returns to the interstellar medium. More importantly, massive stars return a large fraction of their matter to the in…
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