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UT AST 301 - Final Exam Study Guide

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AST 301 1st EditionExam #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 shapeLecture 1- Star clusterso Group them by age, mass, evolve at different rateso High mass stars have shorter length sequence lifetimeso They all have the same distanceo Relative brightness can give us info about their relative luminosity—HR Diagram Plot relative brightnesseso 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 downo 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 fastero Sharp dependence on temperatureLecture 2- Heat transfer: conduction, convection, and radiationo Light is emitted from surface of stars, carrying away energy from the staro 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 Suno Sunspots: hot material dark partso Hotter inside, cooler on the outsideo Hydrogen will be ionized when really hot; plasma o Opacity is what hinders light from making it through a certain regiono Opacity increases as light is flowing outwards - Energy generation in stars: E=mc^2o The helium atom is less massive than the four protonso An equivalence between mass and energyo Basic scheme for how most stars including sun produce most of their energyo Fuses 4 protons into helium atom; helium atom is less massive because the mass is lost in the form of energyLecture 3- Special relativityo Speed of light constant in all inertial frameso It takes much longer for a second to pass since the time is dilated; things are taking longer in high speedo 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 agedo Inertial mass and gravitational mass are nearly the same thing in thiso 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 Evolutiono Energy loss and finite fuel (mass) means finite MS lifetimes (shorter at higher masses)o As core collapses inwards it gets hottero Iron is the heaviest element that can be formed this way by the heaviest starso Outside of core there’s still hydrogen that hasn’t fused yet so it fuses in shells around thecore; so it’s not like all fusion happens in coreLecture 4 - Evolution of starso 97% stars are small, low mass stars. Their final stage is white dwarfso 3% are large stars; final stage is neutron staro Most stars get larger when massive; but more massive white dwarfs get smaller and withtoo much mass the white dwarf squishes and breaks and is not there anymoreo 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 starso Are dim and white, meaning small and hot!o Final stage of stellar evolution for 97% of stars, including our Suno 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 layerso Evolution is simple, they basically just cool offo Dimmest white dwarfs are the coolest and longest lit- Pulsating starso Sun has it in terms of hourso 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 longero Once you have luminosity, you can get its distanceLecture 5- WD+WD Binary with 12.75 min orbito Orbital decay from gravitational radiationo 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/breakso Two normal stars are in a binary pairo The more massive star becomes a giant which spills gas onto the secondary star causing it to expand and become engulfedo The secondary lighter star and the ore of the giant star spiral inward within a common envelopeo The common envelope is ejected, while the separation b/w the core and the secondary star decreaseso The remaining core of the giant collapses and becomes a white dwarfo The aging companiono The white dwarf mass increases until it reaches critical mass and explodes- Black holeso Nothing escapes the event horizono Black holes can bend light to the point where the dip is total; it falls down in the “singularity” forevero 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 allLecture 6- Milky wayo 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 classificationo Elliptical galaxies: more stretched outo Spiral galaxies: different amounts of windednesso Regulars/peculiars: from interactions between galaxies- Galaxy formation/evolutiono Galaxy collisions are more commonLecture 7-


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UT AST 301 - Final Exam Study Guide

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