Overheads2 - Overheads for Lectures Spiral Galaxies spiral...

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Overheads for Lectures: Spiral Galaxies – spiral structure Potential Theory spherical models flattened models Stellar Orbits spherical potentials axisymmetric potentials non-axisymmetric potentials
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Spiral Structure – Winding Dilemma Spiral arms structure would be too tightly wound after  ~1 Gyr due to differential rotation  Eventually spiral structure is “smeared out”
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Density-wave theory – how to maintain star-formation  along spiral arms Density Waves in Traffic
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Spiral arms are caused by the compression of gas as it orbits  the Galactic center and encounters density waves that are  essentially stationary. Compression of gas causes stars to  form which we see as spiral arms.  Density Waves in Spiral Galaxies •Cloud approaches arm at a relative speed of ~100km/s. •Arm acts as gravitational well, slowing down the cloud. •Arm will alter orbits of gas/stars,
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Overheads2 - Overheads for Lectures Spiral Galaxies spiral...

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