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Lecture

Lecture 21

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Department
Physics
Course
PHYS 183
Professor
Tracy Webb
Semester
Winter

Description
PHYS 183 – The Milky Way Inside and Out – Tracy Webb Winter 2013 Lecture 21: February 27 , 2013 th  we are going to start with star birth  a star birth is more like a formation event  the single most important feature of a star is it’s mass  it determines everything  but what determines the mass of a star?  nebula: large cloud of gas in the universe  interstellar medium: the gas and dust between stars  in the universe where stars form  newborn stars produce white patches in the cloud where starlight illuminates surrounding gas  clouds look dark where dust particles block the light from more distant stars  dust in the universe is tiny little grains of soot-like ash  interstellar medium is a place where you find a lot of extra energy or energy that is being blocked  most of the matter in giant molecular clouds is in the form of molecules 2H , CO) as opposed to single atoms  molecular clouds usually have very distinct boundaries/edges  they have typical temperatures of 10-30 K (very cold) & densities of 300 molecules per cubic cm (best vacuum’s in physics labs are ~100 molecules per cubic cm)  very cold & very dense  interstellar dust is made of tiny solid particles made of carbon, silicon, iron & oxygen  larger than molecules & made of heavier elements  it also blocks the light from stars behind them  interstellar reddening o dust is better at blocking blue light than red o recall: light interacts with orbits larger than it o there is a general ring of apparently red stars at the edge of the molecular cloud o observing the infrared light from a cloud can reveal new stars within it  wavelengths (like infrared) provide a lot of information about hidden processes  dust grains in the gas glows in the infrared since they absorb energy from new stars (anything with a
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