Ast 105 1st Edition Lecture 17Outline of Last Lecture I. Edwin HubbleII. Milky Way Galaxy a. Spiral StructureIII. Galactic CenterOutline of Current Lecture I. Types of Rotationa. Solid-Body Rotation b. Keplerian Rotationc. Differential Rotation II. Reminders: Test 2 a week from today; quiz at end of class today. Observations of the 21 cm spin-flip line of hydrogen reveal the exact nature of rotation velocities of our galaxy. Current LectureSolid Body Rotation - If velocity is a linear function of r (distance from center, radius), we have a solid-body rotation Keplerian Rotation - Plotting speed of planet vs. how far away from sun - If velocity is proportional to “1” over the square root of the distance, said to be keplerian In honor of K3L (“Keplerian rotation”)Differential Rotation These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- We do not fully understand how this interacts with the other two rotations - High order polynomial - Milky Way Galaxy has differential rotation - Our solar system has a velocity of 230 km/second That means we are traveling at about 500,000 mph - Since our solar system 27,000 Light years away from the center of our galaxy: the time tomake 1 complete orbit around the center is 230 million years- Scientists think there must be a giant spherical halo of matter that binds and glues together produces solid body effects and keplerian effects- No signal we can see comes from this matter dark matter Gives off no signal, yet we believe it is there due to the effects that we see - About 90% of the galaxies mass must be dark matter A fraction of that dark matter could be neutrinos Other possible candidates include small black holes, brown dwarfs, etc… Mostly, dark matter would have to be exotic
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