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The Interstellar Medium and Star Formation Material between the stars – gas and dust

The Interstellar Medium and Star Formation

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The Interstellar Medium and Star Formation . Material between the stars – gas and dust. Interstellar Dust -- the general obscuration and discrete dark clouds. Dark nebulae. Dust grains cause dimming and reddening of starlight due to absorption and scattering of light - PowerPoint PPT Presentation

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Page 1: The Interstellar Medium and Star Formation

The Interstellar Medium and Star Formation

Material between the stars – gas and dust

Page 2: The Interstellar Medium and Star Formation

Interstellar Dust -- the general obscuration and discrete dark clouds

Dust grains cause dimming and reddening of starlight due to absorption and scattering of light

Scattering is wavelength dependent – blue light scattered more

Dark nebulae

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Reflection nebulae -- dust grains reflect the light of embedded stars

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Interstellar gas -- how do we “see” the gas?

Exists in both cold (neutral hydrogen H I) and hot ( ionized hydrogen H II)

“hot” gas – diffuse or emission nebulae – H II regions

Photoionization – hydrogen ionized by UV radiation from embedded hot, young stars

Free electrons captured and “recombine” with atom – producing emission as electron cascades down through energy levels

Cold or H I (neutral) gas – produces an emission line at 21 cm – detected in radio

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H II Regions

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The Orion Region

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Interstellar Molecules and Giant Molecular Clouds (GMCs)

Numerous simple and complex molecules found in ISM - in cold, dark clouds, concentrated in the dark nebulae especially in the GMC’s

GMCs -- Very large & massive - > 100 pc in diameter,

105 -- 106 Msun

Sites of star formation

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Star Formation

Sites – cold, dark clouds of dust & gas

Gravitational collapse

Small dense core forms first

Heat of collapse trapped,

Escaping radiation seen in infrared

“Protostar” -- star in formation, no nuclear reactions

- a strong IR source, embedded in dark nebulae

Examples – dark “thumbs” in H II regions, small dense globules

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M16 the Eagle Nebula – “Pillars of Creation”

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Stars in formation surrounded by material from the nebula, eventually collapses into a disk – recall Solar nebula

Images of young stars surrounded by circumstellar disks and jets of material -- both accretion and bi-polar outflows -- Herbig-Haro objects

Eventually photosphere heats up,

Becomes visible – a pre-main sequence object

When central core reaches 107o K nuclear reactions – p-p chain begin

For a star like the Sun – 30 x 106 yrs