Star Formation (Compare: Solar System Formation)

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Star Formation(Compare Solar System Formation)
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Where Stars come from the Interstellar Medium

• Gas
• Single atoms and molecules
• Mostly hydrogen (90), 9 helium deficient in
  heavier elements
• Dust
• Microscopic clumps of atoms/molecules
• Size 10?7 m, similar to the wavelength of
  visible light
• Composition is not well known
• Temperature depends on the proximity of stars,
  typically 100 K
• Density is very low!
• Gas about 1 atom/cm3 D Dust even less
  dense

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How do we know its there?

• Cold gas or dust doesnt glow
• they are dark
• We might see them blocking light of other
  objects (Dark Nebulae)
• Gas Dust clouds are very dilute
• they might not be blocking other objects light
  totally
• Usually they will reduce (redden) the light of
  other objects

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Reminder Kirchhoffs Laws

• Cool gas absorbs light at specific frequencies
• ? Dark Lines fingerprints of the elements

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Looking Through Dust Clouds
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Seeing Through Gas and Dust

• EM radiation is appreciably scattered or absorbed
  only by particles with size comparable to its
  wavelength (or larger)
• Gas
• Emission and absorption lines
• Doesnt block EM radiation

• Dust
• Grain size is comparable to the wavelength of
  visible light
• Dims visible light and high frequency EM
  radiation
• Transparent to longer wavelength radio and
  infrared radiation, though

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Scattering in Earths Atmosphere
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The Interstellar Medium

• Dust dims and reddens the light from distant stars

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Dust Clouds

• What happens to the blue light scattered by the
  dust clouds?
• Its still there, and sometimes can be seen

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Nebulae

• Any irregularly shaped cloud of gas and dust
• May be bright or dark, depending on temperature
• Types
• Emission (bright) Nebulae
• Dark Nebulae
• Reflection Nebulae
• Historic Remark Only some of the 109 nebulae
  catalogued by Charles Messier in 18th Century are
  actual nebulae most are star clusters and
  galaxies

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Dark Nebulae

• Classic Example Horsehead Nebula in Orion

Cant see whats behind a dark nebula, thats why
we see it!
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Dark Nebulae

• Dark Nebulae do emit light of their own, though
• Temperatures 10 to 100 K black body radiation
  peaks in the radio to infrared frequencies

fpeak in infrared frequencies
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Dark Nebulae

• Now you see it ? Now you dont
• (infrared frequencies) (visible
  frequencies)

Rho Ophiuchi (infrared)
Rho Ophiuchi (visible light)
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Emission Nebulae

• Regions of hot glowing gas
• Temperatures 8000K
• Made to glow by ultraviolet radiation emitted by
  new O- or B-type (hot) stars located inside
• Emission lines from the nebula are easily
  distinguished from the continuous spectrum and
  absorption lines of stars within
• Color predominantly red, the color of a
  particular hydrogen emission line (the H? line)

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Emission Nebulae

• Example Orion Nebula (M 42)
• hot glowing gas
• Temperatures 8000K
• Made to glow by
• ultraviolet radiation
• emitted by young
• O- or B-type (hot)
• stars located inside
• Color predominantly
• red, the color of a
• particular hydrogen
• emission line (H?)