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Lecture 32

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PHYS 183
Tracy Webb

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PHYS 183 – The Milky Way Inside and Out – Tracy Webb Winter 2013 Lecture 32: April 8 , 2013  mass and energy are essentially the same thing  we do not know what dark energy or dark mass is  despite this we can still quantify its effects  we’ve known about dark matter for almost 100 years but we still don’t know what it is  know what it isn’t though  we can only see it on very large scale sin the universe, so it is hard to study  evidence for dark matter: galaxy rotation curves o you can think of our solar system as a rotational galaxy o you can plot the orbital speed of each planet as a function from their average distance from the sun o you can see that the planets close to the sun move faster than the planets farther from the sun o this is called Keplerian motion o this is different than a wheel rotating where the farther objects move faster as they have farther distances to go in order to keep up  the rotation curve is a straight line, instead of a curve o Milky Way rotation  for rotational velocity to stay constant while radius increases the amount of mass must also increase, but visible matter decreases  can see the orbital speeds or spiral galaxies through Doppler shifts 
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