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IUPUI AST 105 - Exam 2 Study Guide

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ASTRO 105 1st Edition Exam #2 Study GuideTopics (extensive look; not exhaustive, but covers the most important material)Chandrasekhar Limit- Also known as white dwarf limit- Maximum possible mass for a white dwarf is about 1.4 Msun - Electron speeds are higher in more massive white dwarfs Fundamental limit onmax. mass Theoretical calculations show that the electron speeds would reachthe speed of light in a white tour with a mass about 1.4 times the mass of the sun Because neither electrons nor anything else can travel faster than the speed of light, no white dwarf can have a mass greater than 1.4Msunknown as the Chandrasekhar limit- 1940-as long as mass of white dwarf less than 1.4 Msun, electron degeneracy pressure could balance gravity - Our sun will end up as a white dwarfDark matter- Matter that we infer to exist from its gravitational effects but from which we havenot detected any light- Apparently dominates the total mass of the universe- “Cant see it”- Gives off no detectable radiation or signal, yet we believe it is there due to the effects we see/observe- About 90% of the galaxies mass must be dark matter Could be part neutrinos Other possible candidates include smaller black holes and brown dwarfs Would mostly have to be made up of exotic particlesDwarf stars Brown Dwarf- Very small pre main sequence stars- Mass = 10% Msun- Here, gravity is not sufficient enough to start fusion (no fusion occurring)- Jovian’s are brown dwarfs (Jupiter and Saturn)Red Dwarfs- Low mass (mass about 10% Msun)- Main sequence stars- Slowly fuse hydrogen- Surface temps about 3000 K- Can live up to 500 Billion years- Most common in universe- About 1/3 size of our sun White Dwarfs - As outer layers are busted away, the high temp carbon-oxygen core is exposed this forms a white dwarf- Are stable: gravity balanced by electron degeneracy pressure - Stars that have burned up all hydrogen previously used as fuel - Very dense- 1 teaspoon of white dwarf = about 5 tons - This is the last observable stage of evolution for low and medium mass stars  dim, left over star corpses- max. possible mass = 1.4 Msun (Chandrasekhar Limit)Edwin Hubble-1923 photographed M31 (another galaxy called Andromeda)- While examining photo plates, noticed Cepheid’s existing w/in M31 Determined absolute magnitude by observing the periods from bright to dim back to bright, and also the apparent magnitude  Cepheid’s used to estimate distances (pulsations)- Determined M31 was 2.2 million Light years away; another galaxy -Noticedthat in spiral galaxies, the larger the nuclear bulge, the tighter the spiral arms.Galaxies- In our visible universe, there are about 1011galaxies (about 100 billion)- Before 1923, it was thought that there was just one galaxy, ours.- Our solar system is in the Milky Way Galaxy- Galactic center: nuclear bulge in the center of a galaxy  A planet in the bulge will never experience night.- Masses of an average galaxy range from 109 Msun to 1013 Msun - Types of Galaxies Spiral (Flocculent, Grand Design, Barred) Elliptical Lenticular IrregularGalaxy shapes -Spiral Galaxies- Have nuclear bulge ( larger the bulge, tighter the arms)- Have spiral arms- Rich gas discs- Average spiral galaxies have about 1011 stars (100 billion) and are about 100,000 light years in diameter- Types of Spiralo Flocculent: spiral not well defined  Self propagating star formation  New, young stars form near center differential rotation drags inner younger regions ahead of the outer older regions stars die and dim before spiral arms fully develop  Arms fuzzy and cloudy o Grand Design Spiral: spirals well defined Formation explained by spiral density waves Medium undergoing rotationperturbation in the centerwave which propagates radially outward will produce a spiral density wave o Barred Spiral: 2 prominent spiral arms Current data says Milky Way is Barred Spiral  When amount of dark matter is rather small, we see formation of barred spirals  Straight bar of stars cut across center  Spiral arms cut away from ends of bar -Elliptical Galaxies- Have no spiral arms- Range from being circular up to highly elliptical - Have almost no inter-stellar medium (no ingredients to form new stars) “Stars are there, we just don’t see them form”- Vary greatly in size  Some are 20x size of Milky Way -Lenticular Galaxies- Similar to spiral but have no arms- Has nuclear bulge -Irregulars- Have no structures- Cannot be categorized into other shapes/typesGiant and Supergiant stars- Stars in the upper right of an HR diagram - More luminous than main sequence stars of the same surface temp.- Very large in radius - Giants Main sequence stars with masses greater than 40% the mass of our sun become giants when core hydrogen has been converted to helium - Super Giants Arise from main sequence stars (w/ 8Msun < Mass < 25 Msun) form neutron stars after supernova Globular clusters- Spherically shaped clusters of up to a million or more stars- Found primarily in the halos of galaxies Contain only very old starsInterstellar medium - Gas and dust that fills space between stars in a galaxy - Gas composed of mostly hydrogen and helium  Basically ingredients to form new stars- Stars form due to gravitational attraction that binds particles that make up the inter-stellar medium- About 10% of galaxy’s mass is inter-stellar medium - Composition  74% hydrogen, 25% helium, 1% others - Very cold and emits almost no visible light Interstellar reddening- Change in color of star light as it passes through dusty gas - Light appears redder as dust grains absorb and scatter blue light more effectively than red light - Blue/purples have large scattering angles (get bent the most, easiest to scatter) Purple scatters the most, but sun produces very little; blue is dominant This is why our sky is blue and our sunsets are red - The day time sky (on Earth) is blue because blue light is a color that easily scattersMilky Way - 100,000 LY’s across- About 1011 stars - Disc about 1,000 Ly’s thick - Rotating disc of matter  Spiral structure  barred spiral (2 prominent spiral arms)- Center is galactic nucleus/bulge- About 27,000 LY’s away from galactic center- Able to locate center via globular clusters Clusters orbit


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