the interstellar mediumthe interstellar medium • interstellar medium = gas and dust between stars...

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The Interstellar Medium Interstellar medium = gas and dust between stars – Temp ~0 − 300 K (Ave. 100 K) Low density ~10 6 atoms/m 3 gas individual atoms 90% H, 9% He, + trace elements dust clumps of atoms and molecules (like chalk dust) composition not well known (silicates, iron, carbon, ices) 1

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Page 1: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

The Interstellar Medium

• Interstellar medium = gas and dust between

stars

– Temp ~0 − 300 K (Ave. 100 K)

– Low density ~106 atoms/m3

– gas

• individual atoms

• 90% H, 9% He, + trace elements

– dust

• clumps of atoms and molecules (like chalk dust)

• composition not well known (silicates, iron, carbon,

ices)

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Page 2: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

Extinction

• Light from a star going through the

interstellar medium is scattered by the dust.

• Wavelength of light scattered ~ size of dust

particles

• Dust scatters blue light more efficiently

– “reddening”

– Need to use spectral classification to identify

temperature of stars since color can be affected

by extinction.

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Page 3: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

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Page 4: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

Nebulae

• Nebula = cloud of interstellar gas and dust.

– Looks like fuzzy patch in the sky.

– Composition roughly the same as the

interstellar medium.

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Page 5: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

Emission Nebula

• Glowing clouds of hot, interstellar gas

• Each has very hot O or B type star inside.

• High energy photons ionize the gas

• When electrons recombine they emit light.

• Nebula appear red because on of the main

recombination lines of H is in the red

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Page 6: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

Hydrogen

Lines

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Page 7: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

Reflection Nebula

• Light enters nebula and blue light is

scattered.

• Nebula appears blue.

See only blue scattered light

Blue light is

scattered

Star appears

reddened, but

cloud is blue

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Page 9: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

Spider and the Fly

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Page 10: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

Dark Dust Clouds

• Cool (10-20 K) dense clouds made mainly

of gas with some dust.

• Dust obscures visible light.

• Can measure several parsecs across.

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Page 11: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

Dark dust cloud and

reddening

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Page 12: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

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Page 13: The Interstellar MediumThe Interstellar Medium • Interstellar medium = gas and dust between stars –Temp ~0 − 300 K (Ave. 100 K) –Low density ~106 atoms/m3 –gas •individual

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