AST 105 1st Edition Lecture 18Outline of Past Lecture (#18 from March 24)Types of Rotationa. Solid-Body Rotation b. Keplerian Rotationc. Differential RotationOutline of Current Lecture (#19, March 26)Topic: Types of Galaxies - Spiral Galaxies-How Spiral Arms Form -Flocculent Spirals -Grand Design Spirals-Barred Spirals - Elliptical Galaxies- Lenticular Galaxies- Irregular GalaxiesReminder: Test next class, on Tuesday March 31st Galaxy Types- Masses of an average galaxy range from 109 Msun to 1013 Msun - The Milky Way is 1012 Msun - Types of Galaxies:o Spiral o Elliptical o Lenticular o Irregular Spiral Galaxies 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.- Have a nuclear bulge - Have a spiral arms- Hubble noticed that the larger the nuclear bulge, the tighter the spiral arms- The average spiral galaxy has 1011 stars (that’s about 100 billion stars) and is about 100,000 Light-years in diameter - Types of Spiral Galaxies o Flocculent Galaxies Spirals are fuzzy, not well defined Self propagating star formation o Grand Design Spiral Galaxies Spiral arms are well defined o Barred Spiral Galaxies 2 main/prominent arms Current data tells us that the Milky Way is a barred spiral - How Spiral Arms formo Flocculants Self propagating star formation Here, new young stars form near the center and the galaxies differential rotation drag the inner younger region ahead of the outer older regions. Eventually, the stars die and dim before the spiral arms fully develop.- This process leads to “bits and pieces” of spiral arms flocculent structureo Grand designs: Spiral density waves explain formation Have a medium undergoing rotation (think like liquid or gas) perturbation (fluctuation) in the center the wave which propagates radially outward will produce a spiral density wave - “Pie plate with water on a turn table, drop small stone in center small spiral wave Elliptical Galaxies - Have no spiral arms- Range from being circular up to highly elliptical - They have almost no inter-stellar medium No ingredients to form new stars “Stars there, but don’t see formation of new stars”- Vary greatly in size Documented some that are 20x the size of Milky Way Lenticular Galaxies - Similar to a spiral but has no arms Sunny side up fried eggs (picture that)- Have nuclear bulge, but no armsIrregulars- Have no structure Because some galaxies don’t fit into any of
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