Final Exam Study Guide
Final Exam Study Guide AY 101
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This 19 page Study Guide was uploaded by Alyssa Hendrixson on Friday April 24, 2015. The Study Guide belongs to AY 101 at University of Alabama - Tuscaloosa taught by Dean Martin Townsley in Winter2015. Since its upload, it has received 128 views. For similar materials see Introduction to Astronomy in Physics 2 at University of Alabama - Tuscaloosa.
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Date Created: 04/24/15
AY 101 Lecture Notes The Millq Way Galaxy 0 Basic Galactic Structure 0 Major galactic components stars and gas Disk 0 Flat with spiral arms Bulge Central spheroid region Halo 0 Large lowdensity spheroid quothaloquot of old stars and clusters 0 The Sun is a star about halfway out in the disk 0 Satellite Galaxies o A large number of small galaxies orbit the Milky Way and are currently in the process of merging into the Milky Way 0 Merging When stars from two galaxies mix together into one galaxy Very common 0 Scale Sizes 0 But the stars never touch why Recall lecturehall solar system Neptune orbit o This room 0 Sun 0 Smallcircle Jupiter 0 Dot 0 Earth 0 Width of hair On this scale Nearest star about 4 lightyears away is about as far away as Birmingham 0 Change scale 1 light year 1 millimeter Nearest star o 14 inch 0 Galaxy disk thickness 0 1 meter 0 Galaxy disk diameter 0 Football eld Galaxy about 100 billion times mass of sun Nearest other small galaxy about less than 2 football eld lengths away 0 Dark Orbits o Orbits in the disk All nearly the same plane Shorter period at smaller radius but nit Keplerian due to dark matter AY 101 Lecture Notes Oscillate up and down through disk due to disk39s mass Period about 200 million years at Sun39s radius BulgeDisk Orbits 0 Not orientedaligned in any particular way 0 Stars can be orbiting in opposite or completely unrelated directions 0 Star go far away from disk plane 0 Dark Matter 0 More like quotghost matterquot 0 Does not interact electromagnetically can39t bounce light off it 0 Most of our everyday world light solid objects chemistry is due to electromagnetic interactions 0 Makes dark matter very hard to detect only through other forces weak nuclear force gravity 0 Orbital period of a star is determined by the mass enclosed in its orbit o Orbital motions indicate there is more mass than there are stars gas and dust o In a galaxy there is more dark matter than everything else 0 The dark matter halo is larger than the galaxy that lives in it 0 Our Galaxy 0 Different features visible at different wavelengths Spiral Arms 0 Spiral arms in our galaxy are like those in others 0 Are bright due to shirtlived stars 0 Also show dust from starforming regions 0 Star formation caused by spiral density waves in the gasstars orbiting in the disk 0 Density waves 0 Gas and stars move through the spiral arm in which there is a wave of increased density Higher density clouds can form stars Also forms dust Shortlived stars are bright and blue Highmass stars don39t last very long 0 Bright stars mostly in spiral arms Galactic Center 0 Supermassive black hole at center Radio source called quotSagittarius Aquot o The smaller component of a radio source in the constellation Sagittarius Stellar orbits indicate something of 34 million solar masses within a region smaller than the size of the solar system Only real option is a supermassive black hole at the center of the galaxy AY 101 Lecture Notes Components of Galaxies Building Blocks Gas and Stars 0 Stars A group quotpopulationquot 0 Young 0 Blue 0 Because bright blue stars are shortlived Old 0 Red 0 Gas Cold dense dusty Hot lowdensity Components 0 Galaxy structures are made up of stars and gas in particular forms Plus dark matter and black holes 0 Smallscale structures Globular cluster Hll regions Molecular clouds o Largescale structures Disk component Spheroid component bulge halo Dark matter halo Central black hole Globular Clusters 0 Large selfbound clusters with a centrally concentrated distribution of stars 0 Generally are away from disk of galaxy 0 Medium and large galaxies have quotsystemsquot of multiple globular clusters throughout their halos Hll Regions 0 Hot ionized hydrogen gas around highmass stars and young star clusters 0 Often associated with active star clusters for example spiral arms 0 Appear red from the line emission ionized hydrogen 0 Just after star formation 0 Molecular Clouds 0 Contain large amounts of dust Block light from background stars Associated with star formation AY 101 Lecture Notes Common in spiral arms Are evaporated by their own star formation 0 just before star formation 0 Disk 0 Thin component with stars and gas orbiting in the same direction Show spiral structure Can be viewed quotfaceonquot or quotedgeonquot Young stars star formation cold gas 0 Spiral structure due to young stars created by density wave 0 Blobbyness of spiral arms due to individual star clusters Spheroid 0 Almost all stars only a little hot gas Called quotbulgequot in Milky Way and other spiral Negligible star formation 0 Mostly oder longlived stars 0 Galaxies can have various amounts of disk and spheroid components 0 Essentially a galaxies have some spheroid component some have no disk and only a spheroid Dark Matter 0 Largest component of medium and large galaxies 0 Does not interact eectromagneticay Does not emit or block ight Does not quotcollidequot with other particles Only detected by gravity 0 Black Hole 0 Energy comes from matter falling toward black hole Gravitational potential energy 0 All moderate and large galaxies contain a supermassive about 1 million soar masses black hole o In some instances this black hole can be quotactivequot This means it is accreting and generally has jets 0 Depending on perspective of observer the accretion disk may be obscured by dusty gas 0 Radio Lobes 0 Created by jets from active supermassive black holes 0 Contain hot gas and tangled magnetic eld which causes copious radio emission o Phenomenally large scale structures for originating from the compact source AY 101 Lecture Notes Distance and Beginning of Time 0 Distance to Galaxies 0 Before the 19205 the distance to what we call quotgalaxiesquot was unknown 0 They were still called quotnebulaequot and there was a debate Were they inside or outside the Milky Way galaxy o The distance to Andromeda was measured by Edwin Hubble by measuring the period and brightness of individual Cepheid variable stars Cepheid Variable Stars 0 Grows larger and smaller and brighter and dimmer over time 0 Time period closely related to brightness o Calibrated with stars in the galaxy of known distance 0 Showed that Andromeda is far outside our Galaxy 0 Distance and Redshift 0 Was widely known that galaxies showed redshifted spectra was thought to be caused by Doppler shift due to their motion away from us 0 Various distance indicators showed Galaxy recession velocity increases with distance 0 Can infer Universe is expanding Age of universe is nite Recession o More distant galaxies are receding more quickly move farther away in same amount of time o This quotrecessionquot is observed from any galaxy Distance between galaxies is increasing 0 Simple implication All galaxies were zero distance apart a nite time in the past 0 Age of Universe 0 A very simple estimate of the age of the universe How long has it been since the galaxies were all zero distance apart 0 14 billion years AY 101 Lecture Notes Dark Matter and Types of Galaxies Dark Matter 0 Orbital period of a star is determined by the mass enclosed in its orbit o Orbital motions indicate there is more mass than there are stars gas and dust Galaxy Types 0 Elliptical Pure spheroidal component 0 Stars and some hot gas No star formation Old stars Wide variety of sizes Most common type in galaxy clusters Are not necessarily quotsphericalquot Generally more ovalshaped often due to rotational attening making them somewhat quotsquashedquot 0 Spiral Show starforming arms and sometimes bars Also called quotdiskquot galaxies because they have a prominent disk component 0 Also have a spheroid Cold gad and active star formation 0 Most common type outside galaxy clusters 0 Irregular Galaxies without a clear organization 0 Many small galaxies Satellite galaxies Some merger products 0 Usually dusty and starforming Hubble Sequence 0 Based mostly on quotshapequot of galaxy o Elliptical sequence based on quotroundnessquot Related to rotation 0 Two spiral sequences letters abc With and without bar AY 101 Lecture Notes 0 Spiral structure related to diskspheroid ratio 0 Shape related to presence or absence of cold gas and star formation Cold gas disk spiral star formation 0 Giant Elliptical Galaxies 0 At core of a cluster galaxies merge to form one giant elliptical 0 Made up of lots of other galaxies put together Dwarf Galaxies 0 Many orbit large galaxies Mostly spheroid not currently forming stars Many have been quoteatenquot by the dominate galaxy in the past this giving their stars to the larger galaxy Galaxy Histories Environment 0 Evolve and interact o Primordial matter clumps into laments due to gravitational interaction 0 Galaxy clusters near quotclumpsquot where laments cross Field galaxies in smaller laments Filament Formation 0 Structures form from very slight nonuniformity in initial density distribution due to gravity 0 Structures quot ow togetherquot to form large clusters 0 Adds galaxies to clusters over time 0 Empty regions called quotvoidsquot Constant Interactions 0 Galaxy quotformationquot and quotevolution are not as distinct as may seem A presentday galaxy was typically assembled from several or many smaller galaxies or dwarf galaxies A galaxy can change its major components during mergers Galaxies are continuously accreting and merging even outside clusters Forming Types 0 How are ellipticals and spirals formed Real answer not known 0 Spiral Requires enough fresh gas to form the disk 0 Low density andor high rotation Can inhibit star formation enough to allow time for disk to form instead of all gas becoming stars Leads to long time of steady star formation in disk 0 Elliptical Direct Forms right after initial collapse Need to convert all gas to stars very effectively 0 High density andor low rotation Use up all gas right away in star formation AY 101 Lecture Notes 0 Leaves stars and ejects remaining gas 0 Very common for dwarf ellipticals can39t hold their gas 0 Elliptical Mergers Turns two spirals into an elliptical Huge starburst during merger from gas collisions May use up nearly all gas to form stars Remaining gas may be blown away 0 Elliptical Clusters Central regions of clusters lled with hot gas As galaxies fall into cluster their cold gas disk component is stripped by hot gas This ends star formation and converts galaxy to an elliptical o Starbursts Activity uses gas to make stars blow excess gas away due to supernovae Can be caused by mergers or just close passes Structure of the Universe 0 Age of Universe 0 A very simple estimate of the age of the universe How long has it been since the galaxies were all zero distance apart 0 14 billion years 0 Recession o More distant galaxies are receding more quickly Move farther in same amount of time More distant galaxies moving faster 0 This quotrecessionquot is observed from any galaxy distance between galaxies is increasing 0 Simple implication All galaxies were zero distance apart a nite time in the past 0 Expansion 0 How does expansion work if there is nothing to expand into 0 Analogy Earth expands Two cities stay at same latitude and longitude Total surface area of earth increases The structure of spacetime is changing being stretched out as time moves forward Galaxies are moving apart but there is no edge of the universe as far as we can tell Ho zon o The largest distance that can be observed with a nite age universe 0 Light from our horizon has been travelling for the entire history of the universe As best we can tell the universe is in nite or at least much larger than ourhonzon O O O AY 101 Lecture Notes 0 Redshift O O O O Galaxies quotmoving apartquot and quotspace expandingquot are two ways of thinking about the same thing Doppler shift is cause by motion Cosmological redshift is caused by expansion Space is quotbiggerquot today than it was when the light was emitted The wavelength is longer Lookback O Fates 0 Due to nite age of universe and lighttravel time distant objects like galaxy clusters as observed are younger than nearby ones How does the overall density of matter compare to the quotcritical densityquot a few hydrogen atoms per square meter RecoHapse Enough matter to quotpull the universe back togetherquot Coasting expansion Not enough mater to reverse expansion Expanding critically Very close to equal to critical density would be very dif cult to determine the actual answer 0 Measuring Theory 0 O 0 Distance between galaxies vs time Measured with supernova objects of known luminosity 1998 Found expansion rate is increasing Continuous accelerating expansion Indicated most of the universe not made of matter Instead it is made mostly of dark matter Energy of empty space being generated by expansion AY 101 Lecture Notes Dark Matter and Dark Energy 0 Dark Matter vs Dark Energy 0 Dark matter Mass that emits nor blocks radiation otherwise acts somewhat like quotnormalquot matter Presence is inferred from gravitational effect Largest component of galaxies 0 Dark energy Energy of empty space produced as universe expands unlike matter Presence is inferred from accelerating expansion of the universe Largest component of overall universe 0 No direct directions We have not been able to bounce a photon electron or proton off of any of these 0 Summary of Dark Matter Role 0 Observations which display the effects of dark matter incude Orbits in galaxies Cluster gas Orbits of galaxies in clusters Galaxy cluster gravitational lensing Largescale structure laments and galaxy clusters Orbits in Galaxies 0 Solar system Orbital speeds decrease with distance from center most mass is in center AY 101 Lecture Notes 0 Galaxies don39t show this lmplies most of the mass is not centrally concentrated like the light is Clusters 0 Location and density of hot gas in clusters allow measurement of mass due to hydrostatic equilibrium 0 Overall mass is much larger than gas and stars combined 0 Orbits of galaxies un clusters also determine total mass of cluster 0 Much larger than visible matter Cluster Lensing 0 Bending of light by a galaxy cluster provide a measurement of its mass 0 By measuring position and distortion of lensed images we can measure galaxy cluster mass is much larger than galaxies alone 0 Separation of gas normal matter red and dark matter blue in colliding clusters Requires dark matter not modi ed gravity Large Scale Structure 0 With galaxy positions we have measured shape of large structures in mass density 0 Earliest collapsing matter was not interacting with hot photons in early universe just like what we call dark matter What Dark Matter Is Not 0 Normal but fairly inert massive objects such as black hole whote dwarfs neurton stars and brown dwarfs could accounts for some dark matter 0 quotMassive compact halo objectquot MACHOs 0 We can see such objects in our galaxy by their gravitational lensing but no excess of them is observed 0 These do not make up dark matter What Dark Matter Might Be 0 Particle somewhat more massive than photon that interacts very weakly quotWeakly interacting massive particlesquot WlMPs 0 Matches many observations Right structure in early universe Dies not clump on small scales Lenses light on large scales only Dark Energy 0 quotVacuum energyquot Energy of empty space 0 Cases expansion of the universe to get faster and faster possibly eventually pulling galaxies apart 0 Very different and much less is known than dark matter 0 Inferred from the acceleration of the expansion of the universe 0 A necessary component of our understanding if the history of the universe but a poorly understood one 0 Signi cant efforts are going into trying to measure the expansion of the universe in more detail to attempt to improve our understanding AY 101 Lecture Notes Universe Content 0 Makeup of the universe fraction of massenergy Radiation light 0 Very small fraction Normal matter 0 4 Noninteracting quotdarkquot matter 0 23 quotDark energyquot 0 73 0 Both matter and radiation fraction decrease as time moves forward Were much larger in early universe The Big Bang 0 Temperature 0 Temperature higher in dense early universe than now 0 High temperature high density and high energy density in early universe due to compressed state 0 As universe expanded energy spread out and things cooled off Epochs o Uncertain eras depend on some physics that we do not understand well Planck Era Quantum gravity GUT Era Uni ed strong weak electromagnetic forces Electroweak Uni ed electromagnetic and weak nucear force 0 Understood ears based on physics testable in lab Electroweak Higgs Boson discovered Particle Era Elementary particles 0 Photons quarks electrons etc AY 101 Lecture Notes Ear of Nucleosynthesis Helium formation Era of Nuclei Opaque to photons Eras of Atoms transparent Uni cation o Matter particles Electron and other leptons quarks neutrinos 0 Each force has a corresponding particle Electromagnetism Photon Strong nuclear force Gluon Weak nuclear force 0 W Z bosons Gravity Graviton particle nature of gravity still uncertain o Higgs boson eld Long ost brother of photon and weak boson Gives mass to electrons and quarks At high temperatures particles will often have enough energy to easily change into other particles energy is like mass E mc2 For E is greater than mc2 Particles od mass m easin created and destroyed They become part of all interactions Forces hat were separate at lower energy become quotmixedquot Uncertain Epochs o Planck Era Era of quantum gravity 0 Energy density is so large that spacetime itself if dynamic o GUT Era Grand Uni ed Theory of force all but gravity acting In ation thought to occur and quotsmooth outquot the universe 0 Eectroweak Era strong weak and eectroweak force separate Understanding of this physics improving as Higgs Boson is better measured 0 quotModernquot Epochs 0 Particle Era Quarks begin to assemble into protons and neutrons Ends with the matterantimatter annihilation leaving matter 0 Era of Nucleosynthesis Protons and neutrons have formed still hot and dense enough for fusion t make helium and lithium o Era of Nuclei Primordial nuclei have formed O 0000 AY 101 Lecture Notes Electrons still free Universe if opaque to photons o Era of Atoms Electrons are captured to form atoms Universe becomes transparent and photons free stream Helium 0 As universe cools protons become more common because they require less mass energy 0 Extra neutrons captured with protons and fused into helium 0 Temperature and density decrease too fast for much fusion Leave primordial hydrogen and helium and some intermediates Hydrogen2 Lithium7 Transparency 0 When the universe was about 3000K no longer hot enough to ionize hydrogen photons began to move freely 0 We still see the quotglowquot that is those photons o The most distant light source we can observe o Redshifted to now mostly in the millimeter radio wavelength quotCosmic Microwave Background CMBquot Temperature 0 Nearly perfect thermal radiation spectrum redshifted form infrared to radio wavelengths 0 One of the major predictions of the big bang model Expanding universe Hot early universe Should see those photons o Discovered almost by accident during radio receiver development 0 Structure 0 Some properties of the early universe can be inferred from the hot and cold spots 0 Size and shape of dense regions indicated dark matter was not couples to photons quotnonbaryonicquot 0 Overall uniformity and argument for in ation AY 101 Lecture Notes Cosmic In ation Summary of In ation 0 Hot early universe followed by expansion 0 Explains properties of the current state of the universe in terms of speci c early conditions and dynamics 0 Several observed properties remain unexplained How did different regions of the universe which do not even know about each other yet know to have the same kind of initial state How was the lumpiness that grew into galaxies and clusters created Why is the universe not curved of large scales Uniformity o The cosmic microwave background is nearly uniform on scales that had no common history when its light was emitted 0 Without common history a regions could not communicate its state temperature to nearby regions and cause them to be similar Flatness AY 101 Lecture Notes 0 Using wellknown physics of hot gases it is possible to calculate the size of certain features visible in the microwave background 0 Bending light changes observed separation of regions 0 If the observable universe within the hoisin were for example on the edge of an extremely large cluster light paths would show curvature but they don39t Lumpiness o Hotspotslumps arose from well characterized initial conditions Nearly scaleinvariant random speci ed by just 2 parameters 0 Scaleinvariant means look the same in a statistical sense zooned out as zoomed in sometimes called quotfractalquot Flat expansion 0 Expansion driven by something like dark energy as fast enough faster than light to make regions which had common history spread apart and appear not to 0 Essential necessity requiring in ation theory Universe is uniform because it used to be all is historical contact and in equilibrium 0 Early spacetime expansion was different than what we see now Much faster 0 Early phase of fasterthanlight expansion separated regions that used to have a common history When 0 In ation occurred during the uncertain eras Plank and GUT Eras Explanations 0 In ation accounts for each of Uniformity on large scales Flatness Type of nonuniformity 0 In ation is an early epoch of very fast expansion during the GUT era 0 This is the real mysterious quotbirthquot of our universe the region within our ho zon Our understanding of physics I and before the epoch is incomplete Stretching 0 As space quotin atesquot any curvature is stretched out until our local regions within the horizon is at 0 Very remarkable to get both uniformity and atness from the same theory 0 Hallmark of a useful theory Multiple independent prediction results consistent with observations Quantum Lumps 0 Quantum uctuation in energy density during prein ation times stretched by in ation 0 With the right parameter result is similar to the initial lumpiness inferred from the cosmic microwave background 0 Even the deviation from scaleinvariance is predicted AY 101 Lecture Notes Microbial Life in the Universe 0 History 0 Earliest evidence of microbial life dates from 35385 billion years ago 0 On geological timescale this is immediately after the ate heavy O bombardment the earliest that life could possibly have existed Seems to imply that microbial life is formed quite easily or maybe predated solar system Extremophiles O O O Earliest living organisms Organisms with a metabolisms based on a variety of chemical processes that exist in extreme environments Formed around various heat and nutrient sources in the primordial Earth AY 101 Lecture Notes 0 O O O O O O O O O Ancestry DNA and RNA The quotcookbookquot cells use to perform biochemical functions By comparing cookbooks we can nd whose recipes were copied and from whom As time goes by small changes mutations occur leading to changes in traits and evolution Building Blocks Basic building blocks of life Various simple carbon compound Formed quite easily if a mineralrich gas like what would be common on a young earth or many other places is exposed to electrical discharge lighting Carbon compounds are very common in the universe In hot water on certain surfaces these carbon compounds could self assemble into replicating structures Development By starting from basic ingredients we can reconstruct a chain of processes that can lead to life Some details are pretty sketchy hard to test in the lab due to long timescales involved Most steps seem fairly generis if a few basic ingredients are present Heat carbon compounds and liquid water Solar System Candidate site for liquid water include Past and maybe subterranean Mars Moons ofJupiter Particularly Europa All of these places are particularly dif cult to inspect directly Hypothesis of life is largely untested No life found yet but we haven39t been able to look in the most likely places 0 Other Stars 0 O 0 All stars have a quothabitable zonequot in which roclq planets will have liquid water on their surface It appears that earthlike planets are common and we know sunlike stars are common billions in the galaxy Given that microbial life began almost immediately on Earth it seems that it should be common the in Galaxy or perhaps even predate the Solar System Ra re Earth 0 Possible unique things about Earthsolar system Position in galaxy Jupiter reducing asteroid impacts Stable climate 0 Large moon 0 Plate tectonics AY 101 Lecture Notes 0 But each of these might also be fairly general or only modestly unlikely features 0 Also some might only adversely affect complex multicellular life
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