lecture11

lecture11 - Interstellar gas & dust / star formation...

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Interstellar gas & dust / star formation M51
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Milky Way NGC 891 -- a similar galaxy viewed Edge-on
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Two major galaxy components : in Milky Way, stars (~90%mass) interstellar matter (10% of mass) Interstellar matter important – formation of new stars/planetary systems used to study properties of galaxies effects strongly appearance of galaxies also – most beautiful !
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ISM -- interstellar matter 1) (99%) gas -- H, He, +0.1% heavier atoms (eg. CNO) 2) (1%) dust grains -- solids graphite or silicates dust grains : radius ~10 -5 cm (0.1 μ m) absorb visible light very effectively less absorption at longer wavelengths grains in aerogel from star short λ light absorbed & scattered more effectively ==> reddening of background stars graphite & silicates
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optical ( λ =0.5 μ m) infrared ( λ =2 μ m) λ =850 μ m dust emission Dust : What you see depends on wavelength e.g. Barnard 68 -- dust cloud Planck black body emission : λ peak = 0.289 / T cm for dust T ~ 30K ==> λ peak ~ 100 μ m short λ photons absorbed longer λ photons less absorbed ==> see through cloud at very long λ ==> black body emission of grains
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Gas -- characterized by phase of H : HI -- atomic H observed by 21-cm HI spin Fip transition HII -- ionized H
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lecture11 - Interstellar gas & dust / star formation...

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