UT AST 301 - Final Exam Study Guide (4 pages)

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Final Exam Study Guide

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Final Exam Study Guide


Study Guide
University of Texas at Austin
Ast 301 - Introduction to Astronomy
Introduction to Astronomy Documents
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AST 301 1st Edition Exam 4 Study Guide The same repeat questions from previous exams Moon moves counter clockwise Sun is highest in the sky at noon furthest away at midnight 26 Hubble s tuning fork galaxy classification classified galaxies by their shape Lecture 1 Star clusters o Group them by age mass evolve at different rates o High mass stars have shorter length sequence lifetimes o They all have the same distance o Relative brightness can give us info about their relative luminosity HR Diagram Plot relative brightnesses o Hydrostatic equilibrium Sun doesn t change dramatically Things being pulled inwards by gravity but gas pressure pushes outwards creating equilibrium Pressure increases on the way down o Kinetic theory of gases Pressure on walls collisions Temperature kinetic energy speed 2 Boyle s law Pressure proportional to density Charles Law Pressure proportional to temperature Hydrostatic equilibrium pressure gravity Higher temperature means you can fuse energy into core much faster so producing more light at the surface so brighter stars thus shorter lived because they are burning up their fuel much faster o Sharp dependence on temperature Lecture 2 Heat transfer conduction convection and radiation o Light is emitted from surface of stars carrying away energy from the star o Convection things heat up they tend to expand and become less dense heat and pressure are related from Charles law warmer object because less dense thus buoyant and can float If warm air near a heat source is less dense it moves upward and the cool around it will fall under it to fill that space and then that air will warm up and become buoyant and process repeats Energy flow in the Sun o Sunspots hot material dark parts o Hotter inside cooler on the outside o Hydrogen will be ionized when really hot plasma o Opacity is what hinders light from making it through a certain region o Opacity increases as light is flowing outwards Energy generation in stars E mc 2 o The helium atom is less massive than the four protons o An equivalence between mass and energy o Basic scheme for how most stars including sun produce most of their energy o Fuses 4 protons into helium atom helium atom is less massive because the mass is lost in the form of energy Lecture 3 Special relativity o Speed of light constant in all inertial frames o It takes much longer for a second to pass since the time is dilated things are taking longer in high speed o Earth observer sees light travel farther than does the astronaut o Twins send one off in high speed journey they re still young when they come back but everyone else has aged o Inertial mass and gravitational mass are nearly the same thing in this o If the gravitational force is great enough the light will bend down General relativity Light must lose energy as it leaves that well Post MS Evolution o Energy loss and finite fuel mass means finite MS lifetimes shorter at higher masses o As core collapses inwards it gets hotter o Iron is the heaviest element that can be formed this way by the heaviest stars o Outside of core there s still hydrogen that hasn t fused yet so it fuses in shells around the core so it s not like all fusion happens in core Lecture 4 Evolution of stars o 97 stars are small low mass stars Their final stage is white dwarfs o 3 are large stars final stage is neutron star o Most stars get larger when massive but more massive white dwarfs get smaller and with too much mass the white dwarf squishes and breaks and is not there anymore o Neutron stars are really dense objects even if they may not be that big the most dense are black holes through which light can t even escape because the light doesn t have enough energy to escape so its forever bent backwards White Dwarf stars o Are dim and white meaning small and hot o Final stage of stellar evolution for 97 of stars including our Sun o Very dense Mass of the Sun in the size of the Earth Or an elephant the size of a marble Electrons are degenerate require QM to understand o C O cores with thin HE and H outer layers o Evolution is simple they basically just cool off o Dimmest white dwarfs are the coolest and longest lit Pulsating stars o Sun has it in terms of hours o If you turn off pressure structure of Sun and let everything collapse into black hole it would take an hour White dwarf aster seismology can tell us about temperature age etc Cepheid period luminosity relation luminosity increases as period of variability days gets longer o Once you have luminosity you can get its distance Lecture 5 WD WD Binary with 12 75 min orbit o Orbital decay from gravitational radiation o Gravitational radiation carries energy so measuring decay from that The progenitor of a type IA supernova don t worry about type o You take a white dwarf and keep adding mass but keep it less than 1 4 mass which is when the mass is too much and it just explodes breaks o Two normal stars are in a binary pair o The more massive star becomes a giant which spills gas onto the secondary star causing it to expand and become engulfed o The secondary lighter star and the ore of the giant star spiral inward within a common envelope o The common envelope is ejected while the separation b w the core and the secondary star decreases o The remaining core of the giant collapses and becomes a white dwarf o The aging companion o The white dwarf mass increases until it reaches critical mass and explodes Black holes o Nothing escapes the event horizon o Black holes can bend light to the point where the dip is total it falls down in the singularity forever o Stars that can bend light and just change its path and still release the light are NOT black holes black holes don t pass energy through it at all Lecture 6 Milky way o Lots of gas and dust in the middle bulge We can tell there s a super massive black hole somewhere in the mass Super novi re enrich the interstellar medium with metals and is incorporated into the next generation of stars Population 1 stars are the newer stars formed when there were more metals Population 2 stars are the older stars formed when there were less metals Morphological galaxy classification o Elliptical galaxies more stretched out o Spiral galaxies different amounts of windedness o Regulars peculiars from interactions between galaxies Galaxy formation evolution o Galaxy collisions are more common Lecture 7 Supermassive black holes o Can be active sometimes called active black nuclei o Not all are active at the moment o Same

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