lecture9 - Star Birth and Life B ir t h L if e Raw material...

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Star Birth and Life Birth Raw material Protostars Brown dwarfs Demographics Life basic story low-mass stars (<2 M sun ) high-mass stars (>8 M sun ) supernovae intermediate-mass stars (2-8 M sun )
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Star Birth
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Think/Pair/Share How do we know a picture is of a star- forming area? A. It has very blue stars B. It has very red stars C. It has very faint stars D. It has very low-velocity stars
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Raw Material interstellar space typically has 1 atom per cm 3 . Compare to density of air on Earth, ~5x10 22 relatively dense clouds (300-10,000 atoms cm 3 ) form molecules, dust, stars
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Dust very small (<1 m m) agglomerations of C,N,O,Si,Fe. Not the same as dust in your house! dust absorbs short (relative to itself) wavelengths of light, scatters intermediate wavelengths, and has no effect on long wavelengths =>radio/IR observations very important
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Dust in Action (compare to in-class demo)
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Light scattering demo Why is the sky blue and the setting sun red? A. The sun is a red star. B. Red light is scattered more than blue light. C. Blue light is scattered more than red light. D. Blue light has more energy than red light.
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IR/Radio Sees Through Dust (see also movie)
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Birth gravity causes a dense cloud to contract that causes heating, but contraction continues because the heat escapes . (role of molecules, dust, density) lumps within the cloud collapse more to form individual protostars . A protostar has not yet started fusion, but it is hot from its gravitational collapse. Its collapse has stopped because the heat can no longer escape.
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Protostars still surrounded by some gas which has not yet fallen in some gas can be blown away by radiation and stellar winds (possibly from other stars)
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Protostars conservation of angular momentum makes a disk form dense lumps may form planets less dense gas eventually blown away by stellar winds
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Protostellar Disks (same thing as protoplanetary disks)
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Binaries/Multiples Stars are born close together, much closer than typical separation of 2 random stars in our neighborhood Some form binaries or multiples. Systems disperse due to gravitational encounters (ref. reading quiz)
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From Protostar to Star becomes a “real” star when core reaches 10 million K and fusion starts
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Higher-mass Stars Do It Quicker
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lecture9 - Star Birth and Life B ir t h L if e Raw material...

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