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Week 9/ Unit 9: Chapter 12

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PHYS 1600
Mike Massa

Unit 9The Birth and Evolution of StarsProtostarsTeachers NotesThe premainsequence phase is the period when the material that will form the star is organized in some way and becomes an entity followed by a period of evolution into a starTextbook Notes121Gas and Dust Exist Between the StarsInterstellar Medium matter gas and dust existing between the starscontains 10 of the observed mass in our galaxymost is too cold to be seen optically and must be seen through infrared and radio telescopescomposed of gas containing isolated atoms and molecules and tiny pieces of dust90 Hydrogen 9 Helium and 1 metals all other elementsCO CO HO NH HCO CHO2232242new stars form from this interstellar mediumastronomers map out the interstellar medium to look for new starsReflection Nebula a comparatively dense cloud of gas and dust in interstellar space that is illuminated by a star between it and Earth appearing as a bluish hazeNebula a dense region of interstellar mediumoften embedded in much larger bodies of gas and dust called Molecular Cloudslargest clouds called Giant Molecular Cloudsthey contain upwards of a million solar masses of matter and extend up to 300ly acrossDark Nebulae clouds of interstellar medium that obscure the light of more distant stars prevent light from distant stars from reaching uslook like empty space but are one of the most dense forms of interstellar mediumEmission Nebulae glowing gaseous nebulae whose light comes from fluorescence caused by a nearby star an exploding star or a collision between nebulaeInterstellar Extinction the dimming of starlight as it passes through the interstellar mediumsimilar to how clouds on Earth block sunlightInterstellar Reddening the reddening of starlight passing through the interstellar medium resulting from the scattering of short wavelength light more than long wavelength lightthe more gas and dust between us and the star the redder the star appearsdifferent from Doppler Shift the wavelengths we receive arent altered but intensities areAstronomers use radio and infrared telescopes to find nearby interstellar mediuminterstellar medium is a blackbody and are too cold to emit much visible lightJeans Instability the condition under which gravitational forces overcome thermal forces to cause part of an interstellar cloud to collapse and form stars and planetsstars form from gas and dust that become Jeans Unstablemost of this matter is hydrogen in the form of molecules not atomshard to detect in space so astronomers search for cold interstellar gas in the form of COcarbon monoxide emits lots of photons at microwave lengthsthere are 10000 hydrogen molecules for every carbon monoxide molecule in medium
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