Concepts-Week11.ISM - The Interstellar Medium (ISM) A...

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The Interstellar Medium (ISM) A general view of the nighttime sky and of the Milky Way: Stars and Nebulae The presence of an interstellar medium Dust Gas Cool Hot General properties: Average temperature about 100K and densities about 1–10 atoms/cm 3 , typically atomic Hydrogen ( HI ) and about 1000 dust particles per cubic kilometer! dust about 1% of the mass of the ISM. Composition of ISM: about 90% hydrogen, about 9% helium; about 1% heavier elements The Dust Dust grains block light, large dark ’rifts’ in Milky way light Dust grains heated by stellar radiation, dust of Milky Way bright in infra-red. Dust grain size about 1 micro-meter (micron), comparable to wavelength of light Dust: obscures reflects scatters blue light more effectively than red light, interstellar reddening alignment of dust grains, interstellar magnetic field What is a dust grain? core: Iron?, Silicates?, Graphite? — all three? mantle: ices of water, methane, ammonia, carbon dioxide
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This note was uploaded on 01/20/2012 for the course AST 1002 taught by Professor Dr.haywoodsmith,jr during the Spring '07 term at University of Florida.

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Concepts-Week11.ISM - The Interstellar Medium (ISM) A...

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