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HW4_GalaxyRotationDarkMatter

HW4_GalaxyRotationDarkMatter - Galaxy Rotation Curves and...

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Galaxy Rotation Curves and Dark Matter The stars, gas and dust in a galaxy rotate about the center of the galaxy. We would like to know exactly how to describe the rotation of all parts of the galaxy. In other words, we want to know if galaxies rotate like merry-go-rounds, or like planets orbit the Sun, or in some other way. 1. Below are four graphs that show speed versus distance from the center. Which of these graphs best represents how a plot would look for the speeds of points on a merry-go-round and which best represents how a plot would look for the speeds of the planets in our solar system? CAPER T EAM L ECTURE -T UTORIALS FOR I NTRODUCTORY A STRONOMY D RAFT E DITION , 2005 1 Di sta nc e Sp ee d A Di sta nc e Sp ee d B C Distance Sp ee d Sp ee d Distance D

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Distance M as s Galaxy Rotation Curves and Dark Matter 2. Where is the majority of the mass in our solar system? (In what object?) We know that the overwhelming majority of the mass of our solar system is in the Sun and that all the planets are gravitationally bound into orbits around the Sun. We also know that planets located closer to the Sun travel faster than planets further from the Sun. As a result, we find that the graph showing the rotational speed of the planets versus distance will look very similar to the graph showing the distribution of mass in the solar system. Namely that the amount of mass near the center of the solar system would be very high (due to the Sun) and as you move away the amount of mass found in any region gets smaller and smaller because the planets are separated by larger and larger distances.
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