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Final Exam Study Guide - Units 2 and 3

by: annehohler

Final Exam Study Guide - Units 2 and 3 1101

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This study guide includes units 2 and 3 (I retyped 2). Pogge's exam notes are highlighted + graphs, charts, pictures, and tricks to remembering concepts.
Planets to Cosmos
Dr. Richard Pogge
Study Guide
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This 74 page Study Guide was uploaded by annehohler on Saturday December 12, 2015. The Study Guide belongs to 1101 at Ohio State University taught by Dr. Richard Pogge in Summer 2015. Since its upload, it has received 64 views. For similar materials see Planets to Cosmos in Astronomy at Ohio State University.


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Date Created: 12/12/15
Astronomy Final Study Guide 1 Unit 2 Matter and Light —Absolute Kelvin (K)Temperature Scale - Measures internal energy content (temperature) - in gases: the higher theT, the higher average kinetic energy Range of Kelvin 0 K absolute zero (all motions stop) 273 K pure water freezes (~0 Celcius) 300 K room temperature 310 K average temperature of a person 373 K pure water boils (~100 Celcius) Laws of Light (Kirchoff’s Laws of Spectroscopy 1. If a light source is a hot, dense gas => continuous spectrum (blackbody spectrum) 2. If light source is viewed through cool gas => absorption line spectrum 3. if light source is a hot, not-really-dense gas => emission line spectrum #DUQTRVKQP▯NKPGU▯CPF▯ - blackbody: “physical” body that absorbs electromagnetic radiation (light) 'OKUUKQP▯NKPGU▯CTG▯ WPKSWG▯ňHKPIGTRTKPVUʼn▯ VQ▯GCEJ▯KPFKXKFWCN▯ICU ▯ .▯▯▯6 Astronomy Final Study Guide 2 **In a continous (blackbody) spectrum = luminosity is proportional to temperature to the fourth power: Lower K = cooler (redder) and less Luminosity Higher K = hotter (bluer) and more Luminosity ** Maximum wavelength is inversely proportional to temperature ** ** Energy lost => emitted by photons (which have fixed energy and wavelength) Tid-bit: a big orbit = a requirement of high energy; a little orbit = a requirement of low energy ——- Observed Properties of Stars Astronomy Final Study Guide 3 —To find stars, astronomers use a distance ladder. (as you cannot use the same method to find all stars due to varying distances) — you start close to home, then work your way out… •1st Rung: Measure distances to planets with radar -bounce radio pulses off of the planet and measure time -roundtrip time / 2 = one-way travel time -one-way time TIMES speed of light = distance to planet -Measured in astronomical units, or AU. ** AU ~ 149, 597, 870.7 km ** -Distances within the Solar System are known with high precision -The average distance between the Earth and the Sun = “standard unit” of distance. •2nd Rung: Measure distances to stars with parallax *P = parallax angle * *The closer the star = the larger parallax *The further the star = the smaller parallax Astronomy Final Study Guide 4 Parsecs: distance measurement at which a star has parallax of 1 arc-second &KUVCPEG▯ F▯▯▯▯▯A▯ ▯▯▯▯▯▯▯▯▯▯▯▯▯▯▯▯▯▯2▯▯ P = parallax angle ** The next closest star to Earth (besides the Sun) is Proximus Centauri ** ** Parallax Problem: the further the star, the smaller and harder it is to measure the parallax Luminosity: rate at which a light source emits energy; basically the wattage of a star. —> cannot be directly measured; measured with Apparent Brightness, which measures the radiant energy reaching telescopes from a star Inverse Square Law of Brightness: Apparent Brightness + Luminosity Relationship $▯▯▯▯▯.A▯ .▯▯▯▯ŷF $ ▯ ▯▯▯▯▯▯▯ŷF ▯ Nearby stars compute luminosity by observed brightness; brightness depends on distance Astronomy Final Study Guide 5 Solar Luminosity: standard unit of stellar luminosity; adopted value (since Sun’s luminosity changes, but not really…it takes billions of years to change drastically) Lsun = 3.846 x 10^26 watts depends on: 1. Temperature (which also determines the color of said star); “T” 2 2. Surface area; “4∏r ” ▯ ▯ 5QNCT▯.WOKPQUKV[▯▯▯▯ŷT Ͳ6 σ = constant value Examples Star A: 6000 K Star B: 3000 K Stars A and B have the same radius, but different temperatures. Because Star A is 2xs hotter, it is 16xs brighter (6000/3000) = 16 Astronomy Final Study Guide 6 Star C: 6000 K Star D: 6000 K Stars C and D have the same temperature, but different sizes (radii). Because Star D is 2xs bigger, it is 4xs brighter (2/1) = 4 ——— Astronomy Final Study Guide 7 The Hertzsprung-Russell Diagram (or H-R diagram) Stellar Spectra - the hot, dense photosphere of a star is surrounded by a thin, slightly cooler atmosphere - the blackbody emits a continuous spectrum (photosphere); however, the star’s atmosphere creates absorption lines on the spectrum. - color of star depends on temperature (as seen in the graph above) — spectral sequence is a temperature sequence 19th century: discovery that stars can be classified by their spectra - Edward Pickering and his women computers -Willimina Fleming: found spectral pattern; one of the computers Astronomy Final Study Guide 8 -Annie Jump Cannon: found the Spectral Classification Sequence, determined byT Spectral Classification Sequence: O BAF G K M L or… Only Batman Asks For Grey Kites and Much Liquor - O = hottest, 50,000 K - L* = coolest, 1300 K - L was added last ——— Internal Structure of Stars, or “Gas Physics” Physical Properties of Stars: 1. Luminosity (L = 4∏d B) 2. Temperature (color/spectrum) 3. Mass (binary stars - Newton’s 3rd law [period, semi-major axis, and total mass]) 4. Radius (direct imagine - many methods) * Main Sequence (MS) Stars show strong correlation between Luminosity andTemperature, and between Mass and Luminosity ▯ /▯/ ▯ ▯▯▯ .▯. ▯ UWP UWP * Non-MS stars differ in radii—> include Giants, Supergiants, andWhite Dwarfs Main Sequence = Mass Sequence - High Mass MS Stars => High Luminosity, Hot and Blue - Low Mass MS Stars => Low Luminosity, Cool and Red Astronomy Final Study Guide 9 ** Location on MS depends on Mass because of the T/L relationship Mean Density: how compact a star is - MS stars: small range of densities; all aOGCP▯FGPUKV[▯▯ same size because of different - G/SG stars: very fluffy and low density /▯8 ages -WD stars: super compact with high densities Ideal Gas Law: 2▯▯▯PM 6 $ *pressure keeps the stars from collapsing Astronomy Final Study Guide 10 - compress = high pressure - expand = low pressure **Gravity keeps stars from flying apart => gravitational binding increases as radius decreases ' )▯▯▯)/ A▯ ▯ ▯▯▯▯▯4▯ - contract = decreases radius, increases gravitational pull - expand = increase radius, decrease gravitational pull *Hydrostatic Equilibrium: balance between gravity and pressure inside a star Pressure = expansion, pushing out gravity = contraction, pushing in Basic Anatomy of a MS Star: Core: hot, dense, compact; more pressure Envelope: cool, low density gas; extended because of low pressure Astronomy Final Study Guide 11 * Pressure increases the deeper you go into the star—similar to how the deeper you dive into a pool or body of water, the more pressure you feel. * Life of a star is a matter of pressure and gravity being in balance. * Internal changes of a star have external consequences * Stars shine because they’re hot _____ Age of the Sun The lifetime of a star, like the Sun, is a relationship between Internal Energy (how energy is being produced) and Luminosity (rate that energy is being lost). .KHGVKOG▯▯▯+PVGTPCN▯'PGTI[▯▯ ▯▯▯▯▯▯▯▯▯▯▯▯▯.WOKPQUKV[▯ Types of Energy Can fuel our Sun for… Chemical breaking chemical bonds for 20,000 years energy (ie burning shit) utilizing gravity as a force for energy (ie watermills, heat 30,000,000 years Gravitational from meteorite impacts) fusion energy: when 4 protons of H fuses into 1 He Nuclear nucleus, the remaining .7% 10,000,000,000 years becomes energy; occurs inside the core of a star Astronomy Final Study Guide 12 Indication of Nuclear Fusion occuring: Neutrinos can be detected escaping the star - Neutrinos are neutral, unchanged subatomic particles Kelvin-Helmholz Mechanism (for energy inside stars) 1. Starts in Hydrostatic Equilibrium (P=G) 2. Luminosity causes loss in heat/energy; internal pressure drops, and gravity grows stronger 3. Star contracts to balance with the stronger force of gravity; becoming more tightly gravitationally bound 4. Cycle continues, and star shrinks **Radius matters => GM /L 2 star* ———- Energy Generated and Transport in Stars Physics as to how stars work: 1. Hydrostatic Equilibrium 2. Source of Energy 3. Way to Transport Energy from inside, out - Hydrogen Fusion: 1. Proton-proton chain -> for low core, low temperature stars - 98.3% of fusion source in the Sun 2. CNO cycle -> for high core, high temperature stars Astronomy Final Study Guide 13 - 1.7% of fusion source of the Sun ** Carbon is cycled back without it being consumed ** The rate of nuclear fusion is extremely sensitive to temperature. - Hydrostatic Thermostat: self-regulating balance in a star between temperature and fusion rate, preventing explosions. too fast… too slow… the core heats the core cools -> increasing pressure -> decreasing pressure -> causing core to expand -> causing core to contract -> the expansion triggers the thermostat to -> the contraction triggers the thermostat cool the core to heat the core -> slows fusion -> speeds up fusion Three Ways to get Energy from Inside, Out of a Star 1. Radiation: energy carried out by photons 1. the photons zig-zag randomly until it escapes the star’s core 1. example: trying to fight through a crowd going opposite of you 2. Convection: energy carried by bulk increases motions of gas 2. when hot, buoyant gas rises faster than it can radiate heat away 2. example: boiling water 3. Conduction: energy transferred directly from particle to particle 3. dense medium — like v dense 3. example: heating a spoon Astronomy Final Study Guide 14 Normal Stars White Dwarfs - powered by radiation and convection - conduction dominates as energy - conduction => inefficient source - nearly uniform temperature throughout the WD - Thermal Equilibrium: when energy generation is balanced between the generation/ absorption of energy and the transport of that energy to the surface to be radiated away… Energy Generated = Energy Lost More energy generated => star expands Less energy generated => star contracts Astronomy Final Study Guide 15 ———- The Main Sequence **MS Stars fuse hydrogen into helium in their cores **ALSO have Mass-Luminosity Relation —————————> /▯/ ▯ ▯▯▯ .▯. ▯ ▯ UWP UWP In rule JUST FOR MS STARS, the bigger they are, the brighter they’ll be * High Luminosity = hot and blue * Low Luminosity = cool and red * MAIN SEQUENCE = MASS SEQUENCE Internal Structure of MS Stars: 1. core temperature 2. core pressure 3. core composition * As they age, MS stars get slowly brighter and slightly bigger in radius * to maintain pressure, core gets hotter, increasing Luminosity and causing expansion From smallest and dimmest… Red Dwarfs: Mass ~ .08-.4 Msun Astronomy Final Study Guide 16 T core 17 Million K P-P chain fusion only source of energy Lower MS Stars: Mass ~ .4 - 1.2 M sun T core 17 Million K P-P chain fusion dominates * As Mass increases, - inner envelope becomes more radiative - convective outer envelope decreases in size Upper MS Stars: Mass > 1.2 M sun T core 17 Million K CNO cycle dominates core energy * the envelope is less sense, therefore radiative Astronomy Final Study Guide 17 ** Lifespan depends on the mass of the star. - the bigger the star, the more luminous and shorter it’s life - the smaller the star, the less luminous and longer it’s life —————- Star Formation Raw Materials for stars come from GMCs - Giant Molecular Clouds - cold interstellar clouds of H2 - seen as the “black space” between stars (NOTTO BE CONFUSEDWITH VOIDS) - stars form when the clouds break apart in chunks, and when some of those chunks have trapped, they heat up and start condensing to form the protostar! - the chunks are v dense and v opaque to light Birth of Stars: 1. Protostar Phase (10 4-5years) *fastest phase* - forms from built-up pressure - builds up mass by accretion - grows rapidly - steadily establishes Hydrostatic Equilibrium - Hydrostatic Equilibrium ends the phase 2. Pre-MS Star (duration set by Kelvin- Helmholz - depends on MASS) Astronomy Final Study Guide 18 - DO NOTGROW - all energy is from gravitational contraction - steadily establishesThermal Equilibrium - Thermal Equilibrium ends phase * High Mass Pre-MS stars contract rapidly - a star 1Msunwill last ~30 MillionYears in this phase… - but a 30M sunstar will last less than 10,000Years - the core temperature quickly exceeds ~7 Million K - at this point, the star ignites the P-P chain, then CNO cycle - the core quickly ionizes and blows away the remaining gas * Low Mass Pre-MS stars collapse slowly - a star .2Msunwill spend ~1 billion years in this phase - the core temperature reaches 6-7 Million K, which triggers the P-P chain - it then settles slowly into the Main Sequence 3. Zero-Age MS Star =YEAR ZERO OFASTAR - Hydrostatic AND Thermal Equilibrium is reached - all energy from the core comes from Hydrogen fusion Minimum Mass for MS star = .08 M sun(Brown Dwarf) - below this, a star cannot heat enough to start H fusion - they’re very cold and very dim, but “Super Jupiter” in appearance Maximum Mass for MS Star = 100-150 M sun - at this level and above, the core is too hot for equilibrium to occur; it overproduces energy - radiation pressure overwhelms gravity, making the star unstable Astronomy Final Study Guide 19 ——————- Low Mass (< 4M sun ) High Mass #1 (~4-8 M sun) High Mass #2 (> 8 M sun) 1. Zero-Age: H fusing into He 1. Zero-Age: H fusing into He 1. Zero-Age: H fusing into He (CNO cycle) (CNO cycle) 2. Sub-Giant Star: H runs out, 2. Red Supergiant: H becomes Same steps as High Mass #1 2-4 now has He core with H shell a shell around He core; swells in around it radius, is cool and red 3. Red Giant: overproducing 3. Blue Supergiant: triple alpha 3. Mg-Ne-O core fusing Ne energy; loses Thermal fusion of He core; super Equilibrium; becomes 2000xs inefficient brighter, with 165xs larger radius 4. Horizontal Branch: restores 4. Red Supergiant 2.0: now has 4. Neon core fuses Oxygen Thermal Equilibrium with He CO core, is brighter and hotter fusion; stable but short lived than before 5. Red Asymptotic Star: C-O 5. Mg-Ne-O White Dwarf: ejects 5. Oxygen core fuses Silicon core; settles in RA Branch; now envelope, leaving core to 3000xs brighter and ~200xs evaporate with time larger radius 6. C-O White Dwarf: after 6. Silicon core fuses Nickel and thermal pulsations, envelope Iron ejects into planetary nebula and the core eventually cools and fades with time 7. Supernova with Fe-Ni core ** If the star is 8 init 18-20 M sun it becomes a Neutron Star If star is initially > 18-2sun it becomes a Black Hole. Rough look at how different massed stars “age” — full details are in the following pages: Evolution of Low-Mass Stars (M < 4 M ) sun Star formation is very rapid. The formation goes as follows: 1. H fuses into He. Accumulates in core, but stays inert. 2. In maintaining core pressure, the core heats up 3. Higher Temperatures = H fusion runs faster 4. Star brightens and grows in radius to compensate Astronomy Final Study Guide 20 *When H runs out, He core begins to contract, shoving H into a shell around the new He core. It becomes a Sub-Giant Star. * With no source of fusion energy, the He shell heats up and contracts. The H shell can’t compensate because it doesn’t have Hydrostatic Thermostat, so it overproduces energy. * the extra energy shoves the star out of Thermal Equilibrium; the envelope rapidly cools and grows *The star is now a Red Giant. - the process takes 1 Billion years - the star becomes 2000xs brighter, with 165xs larger radius near the end (about the size of the orbit of Venus) Astronomy Final Study Guide 21 * He fusion ignites when the core is ~100 Million K; restoresThermal Equilibrium. The star settles into the Horizontal Branch. - star shrinks and becomes fainter and hotter - stable phase, but short lived (energy lasts ~100 Million years as He core becomes Carbon-Oxygen core) - now a RedAsymptotic Star (when C-O core is formed); takes ~20 Million years to be in RedAsymptotic Branch. * The star now shines brighter and bigger because of fewer and heavier nuclei in the core now 3000xs brighter and ~200xs larger radius * *He shell becomes unstable and drives thermal pulsations in the star. - the pulsations destabilize the envelope (lasts ~400,000 years, and loses 46% of mass in the end) * The core and envelope separate * Astronomy Final Study Guide 22 - the ejected envelope becomes a Planetary Nebula. - ionized by a hot, bare core (C-O core) that burns for 10,000 years - with no source of energy, the nebula cools and fades over time The core => C-OWhite Dwarf - too dense for Ideal Gas Law -Temperature is independent; Pressure now depends on density. Eventually, it fades to nothing. ——- Evolution of High Mass Stars **Live fast and die young** -> sequence is similar to low mass stars, but shorter -> 100% of stars fusion is H to He via CNO cycle in convective core As it ages, it slowly grows in radius and holds near constant Luminosity and Cooler * Temperature Sequence: 1. (~10 million years) hangin’ out on the MS 2. (~1 million years) Post Zero-Age star pushes H shell out for He core. Star moves horizontally on H-R. 1. Becomes a Red Supergiant 1. swells in radius 2. becomes cool and red Astronomy Final Study Guide 23 3. **LUMINOSITYDOESN’T CHANGE** 3. TripleAlpha fusion (He) begins at ~100 million K 1. produced C and O for ~1 million years 2. now Blue Supergiant 1. less efficient (and it won’t become any more efficient from here) 3. (~1 million years) becomes a Red Supergiant…again 1. He has run out in core and become a shell; C-O new core 2. way brighter and way hotter 4. (~1000 years) Carbon fusion occurs with C-O core at ~600 million K. 1. produced Mg, Ne, and He; building up Mg-Ne-O core 2. **If stars mass is ~4-8 M sun this is the end. The envelope ejects and a Mg- Ne-OWhite Dwarf is left behind. Astronomy Final Study Guide 24 5. If star is >8 M sun, it keeps evolving from here, more and more rapidly. Becomes more wasteful and less efficient 1. (~5 years) Neon fusion occurs when Mg-Ne-O core is ~1.5 Billion K; makes dense Ne core 2. (~1 year) Oxygen fusion occurs when Ne core is ~2.1 Billion K; makes Silicon core 3. (~1 day) Silicon fusion occurs when core is at ~3.5 Billion K 1. the core melts into sea of He, protons, and neutrons 2. is using nuclear binding energy at this point, because the nuclei are too heavy for regular fusion; cannot break down any further cores (ends on Fe-Ni core) 3. This is the final phase before it collapses. With the core at ~10 Billion K, there are no more fusion resources of any kind. ——- Supernovae = the last years of a massive (>8 Msunstar’s life after fusion sources have been exhausted. Astronomy Final Study Guide 25 ** the final stages take 1 second. The final core is Fe-Ni; it’s ~1.5-2sunand 10 Billion K; here’s what happens: 1. Photo-disintegration: high energy photons melt into He, protons, and neutrons, reversing the ~10 million years of fusion 2. Neutronization: protons and electrons combine into neutrons and neutrinos. They escape and carry off energy, radically accelerating the collapse of the core neutrinos become trapped in the core (Rstar~ 10 km) Strong Nuclear Force is the core “bouncing”; the core smacks the envelope with a stellar shockwave, stalls, and then the shock flings back and ejects the envelope into a massive explosion—a supernova. - the star brightens to >10 Billion sunwithin minutes, outshining its own galaxy - has been recorded as “guest stars” Supernova Blast Wave: supernova remnants; explosively ejected envelope evolves over 1000s of years (ex. Crab Nebula) Nucleosynthesis: synthesis of core-collapse supernova of massive stars (creation of heavier elements through evolution in space (as there was just H and He in the beginning) ——- White Dwarfs and Neutron Stars What happens with a star’s compact core at the end of its life? - gravity wins and core collapses until - 1. new pressure law halts further collapse and core settles back into Hydrostatic Equilibrium - the collapse continues towards zero radius and infinite density, becoming a black hole. Astronomy Final Study Guide 26 White Dwarfs: collapsed cores left behind by stars with init M suneld up by degenerate electron pressure: M init4 M sun C-O White Dwarf (He fusion) M init4-8 M sun O-Ne-Mg White Dwarf (C-O fusion) Shine only by residual heat — no fusion taking place, they just slowly cool off and disappear Final stage: Black Dwarf, old and cold and hard to detect; takes 1,000,000,000,000,000 years to cool to 5K Chandrasekhar Mass: (Chandra Mass) = 1.44 M sun If M is less than this mass, electron degeneracy failed andWD collapses If M is larger than this mass, it’ll explode as a Thermonuclear Supernova - electron degeneracy fails and collapses - C-O fusion ignites at high density in thermonuclear explosion - fuses explosively to Fe and Ni **The brightest supernova of all, and leaves no remnants** How to exceed Chandra Mass: 1. binary accretion: WD gets matter from a nearby donor star (usually a red giant) 2. double white dwarf merger: two WDs merge; can be induced by the gravity/influence of a third star 3. **DOES NOT HAPPEN NATURALLY** Neutron Stars: collapsed cores left after core-collapse supernovae of massive stars (8 < Minit 18-20 Msun Astronomy Final Study Guide 27 **shines with residual heat; no fusion or contraction By decreasing radial order: white dwarf, neutron star, black hole Pulsars (Neutron Stars): Pulsating Radio Sources - rapidly spinning and magnetized neutron stars - emit sharp millisecond-long pulses every spin period - like lil space lighthouses that spin weird. - slow their spin as they age; gradually losing rotational energy - old neutron stars are hard as Astronomy Final Study Guide 28 hell to find Lighthouse Model of Pulsars 1. strong magnetic field rips electrons off north star 2. electrons accelerate along poles, making two light beams —like a little particle accelerator ——- Black Holes The ultimate extreme object; totally collapsed and no light can escape them; SUPER HEAVY GRAVITY Predicted in Einstein’s Theory of General Relativity (which I’ll get to later) Light cannot escape if it comes from inside the Schwarzschild Radius 4 ▯▯U▯▯▯)/AA▯ ▯▯▯▯▯▯% ▯ Set only by mass—which there is no upper or lower limit for a black hole — the radius of a BH is nearly half the size of a neutron star Schwarzschild Radius defines Event Horizon (aka THE POINTOF NO RETURN) - anything that happens inside Rs is invisible to the outside universe - anything that gets close to Rs can never escape from the BH Astronomy Final Study Guide 29 - gravitational effects only affect other space matter when that space matter is close to the Rs Gravity and BH relationship based on distance: Far Away.. Very Close - Gravity behaves the same as a star - Radius < 3 Rs: no stable orbits; spiral of the same mass in toward BH - if the sun became a black hole, - R = 1.5 Rs: photons orbit in a circle planets would orbit normally. Gravitational Lensing: bends light with strong gravity field around black hole, warping appearances of distant stars and galaxies; like a fish-eye effect in photography Astronomy Final Study Guide 30 How to “see” a black hole: —look for effects of strong gravity on surroundings —look for binary systems where one member is very big but dark —try to detect emitted x-rays (when gas is superheated as it falls into black hole) **Matter falling into a black hole settles into a hot accretion disk that radiates into x- ray light **High-mass x-ray binaries are bright, variable x-ray sources powered by mass accretion, either with massive O or B stars or Neutron Stars or Black Holes Black holes aren’t entirely black—quantum effects shows there’s a slow leakage of subatomic particles that can be seen. but anyway. Hawking Radiation: black holes evaporate very slowly over time by emitting the radiation seen by quantum effects -it’s super cold thermal radiation -the bigger the BH = the colder the radiation and slower the evaporation; small black holes don’t take long ——- Tests of Stellar Evolution The mass of a star tells 1. where the star is on the MS (L andT) 2. how long it’ll live 3. which evolutionary path it follows 4. how its life will end 5. what remnant will be left behind Astronomy Final Study Guide 31 ▯▯▯OKNNKQP▯[GCTU ▯▯▯▯OKNNKQP▯[GCTU ▯▯DKNNKQP▯[GCTU ▯▯▯DKNNKQP▯[GCTU ▯▯▯▯DKNNKQP▯[GCTU ▯▯VTKNNKQP▯[GCTU Life on MS ^^^ Star Clusters: “families” of stars moving together through space; swell things because astronomers can study the history of stars with these suckers. —has a varied population: - can be young or old - have same parent materials/come from same GMC - same distance **show how different masses look at the same age; give puzzle pieces to astronomers that they can work with to piece together the universe Open Clusters: sparse clusters containing 100s to 1000s of stars (like a forest with sparse trees) Astronomy Final Study Guide 32 - loose; eventually drift away from each other as they age because of gravity - Blue MS stars and a few giants - age: oldest is 5 billion years old Globular Clusters: spherical, super packed clusters - oldest is ~13 billion years old - NO BLUE MS OR SUPERGIANT STARS; only red and dead stars - stay together As stars age, they “peel” off of the MS in order of highest mass to lowest. The amount of peel = age of the cluster Astronomy Final Study Guide 33 Unit 3 Island Universes: the Discovery of Galaxies Back to Copernicus…he put the stars in an outermost sphere around the Solar System: the last crystalline sphere - broken by later astronomers, leading the belief that the universe is infinite - MilkyWay: diffuse band of light crossing the night sky (also is our home galaxy - “Celestial River” - “Celestial Road/Path” - can be seen in center of the sky in Southern Hemisphere - the Milky Way is part of every culture’s mythology and belief of place in the universe (ie Inka and “The Four Corners of the Earth”) — Life in the 21st century - we can’t see the Milky Way at night because of the light pollution of today. Galaxy - “Galaxias kuklos” (Milky Band) Milky Way - “Via Lactea” (Road of Milk) - Origin of the Milky Way - nursin’ baby cherubs - One of hundreds of billions of other Galaxies in the Universe * Galaxy: system of many millions of billions of maybe trillions of stars all bound together by gravity * 10s of kilo parsecs in size * distances between galaxies - millions of parsecs (distance on average is 40xs the galaxies diameter) Galileo’s view: it’s made up of an immense number of faint stars (1750)ThomasWright: the appearance of the MilkyWay is due to a flat layer of stars from the inside Astronomy Final Study Guide 34 (1755) Immanuel Kant: the MilkyWay is a rotating, lens-shaped disk of stars centered on the star Sirius - So, the Sun is NOT a special location. **Kant and Wright were only really describing what they saw…** * Other nebulae are distant, rotating “Milky Ways” — Island Universes. (1785) William and Caroline Herschel (siblings): measured the shape of the MilkyWay by counting stars in different directions; made first-ever map of the MW. - also discovered Uranus…but had bigger ambitions than just finding a planet - “star-gauges” - counting stars in all directions - coined term “asteroid” (Pogge’s hero) (1845) William Parsons: discovered the Spiral Nebulae (with a massive telescope - 72-in) - “Parsonstown Leviathan” - some disks were with a spiral pattern - some where edge-on disks with dark bands - none were resolved into stars (1845) Alexander von Humboldt: revived Kant’s “Island Universe” idea; galaxies are made of stars, and are very distant and external to our own galaxy. * the universe is much larger than the Milky Way * * probably coined the term “Island Universe” for the first time tbh; Kant never said those two words together —Crucial Observational Test: demonstrate that the “nebulae” are more distant than the outermost extent of our Milky Way Counter hypothesis: the Spiral Nebulae are swirling gas clouds internal to the MilkyWay —Revival of Solar System formation model by Pierre Simone Laplace (1796) * The Milky Way is the entire universe * (beyond the edge of the stars’ of the MWis just an empty void) Astronomy Final Study Guide 35 * Nebular Hypothesis —Crucial Observational Test: demonstrate that the “nebulae” are nearby and located within the MilkyWay—need… 1. accurate measurement of MW 2. way to measure distances of nebulae (if outside that boundary found in measurements of 1, then they are beyond MWand this theory is faaaalse) Early 1900’s - Jacobus Kapteyn: used photographic star counts and parallax statistics to measure the size of the Milky Way. (using photography - a feat that made trying to decipher what a galaxy is waaaaaaay easier) - Kapteyn Model: the MilkyWay is a flattened disk 17 kilo parsecs (kpc) across, 17000 parsecs, and 3 kpc, 3000 parsecs, thick. The Sun is at 2 kpc, or 2000 parsecs from the center. 1915-1921 - Harlow Shapley: mapped positions of globular clusters; found that the center of the Milky Way is located 16 kpc away from our Sun, toward Sagittarius. * Both over-estimated the size of the Milky Way because they didn’t account for dust absorption. * Interstellar space is filled with gas and dust * Dust absorbs and scatters light, making distant objects appear fainter than actually are * leads to over-estimations of distance based on apparent brightness of stars 1930 - RobertTrumpler: solved this issue 1912 - Henrietta Swan Leavitt: found that key to measuring cosmic distances was based on pulsation periods, which depend on Luminosity. (one of the Harvard computers of Pickett); opened door to measuring stars across galaxies with Cepheid Period- Luminosity Relation - if you can find Period of Variation, you can estimate Luminosity, because pulsation periods are distance independent. Astronomy Final Study Guide 36 - the brighter the star, the longer and slower the pulsation period. - measurement of pulsations is distance independent; distance doesn’t mess with the pulsation period Great Nebula in Andromeda: largest spiral nebula; observational battleground in 1920s. - search began for trying to resolve Andromeda into stars and estimating distance from the Sun, becauseAndromeda will have the answers to the secrets of the universe (it’s super bright and visible to the naked eye, so it must be very close therefore can be watched and recorded) 1923 - Edwin Hubble: answered the question by finding Cepheid variable inAndromeda; used 100-in telescope to photographAndromeda for supernova to prove stars in - found one “nova” that was the Cepheid variable (they’re massive supergiants that pulsate rapidly) - then found 9 more, and found that distance toAndromeda is ~1 Million parsecs - overestimated distance toAndromeda because of dust and gas again —— ATale of Two Galaxies: The Milky Way andAndromeda Sizes of galaxies range from 1 kpc up to many 10s of kpc Masses range from 10^6 to more than 10^12 the mass of the sun - Milky Way - 200 billion stars (# of Oreo cookies made since company began) The MilkyWay is our home spiral galaxy (spiral because it looks like a pinwheel) - it’s a flat disk of stars and gas, with a central bulge—all within an extended spheroid Astronomy Final Study Guide 37 - *in the Northern Hemisphere, living inside a galaxy is a difficult concept to grasp because we cannot see the rest of the galaxy - it’s 10-15 degrees above our horizon. Easy to see in Southern Hemisphere - the disk is ~30 kpc across and ~300 pc thick - the center is obscured by dust in the plane of the Galaxy - in infrared and radio waves, dust becomes transparent; how we view past the dust - our Sun orbits the center at a radius of ~8 kpc — little over halfway out from center to the edge of the disk - orbit: ~240 million years Andromeda Galaxy (called for centuries the Andromeda Nebula) - nearest bright spiral galaxy to the Milky Way - Distance: ~700 kpc - really similar to the MilkyWay; used as a proxy because they’re nearly identical - can test hypothesis about our galaxy and compare toAndromeda to see how accurate we are, as we can see an outside view of Andromeda Spiral Galaxies - have 3-part structure - Disk - flattened disk of stars, gas, and dust - disk of stars: mix of young and old stars; open clusters and loose associations of stars - thin disk of gas and dust: mostly cold atomic H gas; dusty giant molecular clouds (H2); regions of new star formation - Bulge (Central Spheroid) Astronomy Final Study Guide 38 - where the disk and inner spheroid merge - difficult to study because they’re really mysterious and super far away - Spheroid - sparse outer halo of old metal-poor stars and globular clusters - sites of active, recent star formation; hot O and B stars, molecular clouds, and ionized gas nebulae like “beads of string” on the “spiral arms” of the edges the galaxy - look the way they do - pinwheel - because the slightly elliptical orbits of each star are a bit off from one another, creating a natural spiral, or “waves” How the Cloud Arms Work (where the gravity is higher in the galaxy) * H2 cloud enters the spiral arm and get compressed * the cloud fragments and collapses, forming new stars * all stars (high to low mass) move together through the arm * OB stars explode as supernovae… * and lower mass stars keep moving… ** hot stars are only found close to the spiral arms ***stars organize themselves by color… 1940s: Walter Baade - first red- and blue-light photographs ofAndromeda; identified two distinct Stellar Populations based on color and location in the galaxy - because ofWWII, he had the telescope to himself due to his German roots and LA was mostly dark all the time because of bombing fears, so he was an at advantage for astronomical endeavors. 1. Disk Stars - disk looks blue - have H-R diagrams like open clusters (young stars form here) 2. Spheroid and Bulge Stars Astronomy Final Study Guide 39 - look red - have H-R diagram similar to globular clusters (old stars hang out here if they haven’t supernova’d yet) Type of Star Composition Location and Age Chemical Evolution Population III no metal: 75% H, first stars in the 1st generation stars; 25% He, no metals galaxy; none have no metals, no CNO; (anything C and been found; would be just H and He above wouldn’t be very, very faint today; seen) potentially in the spheroid Population II metal-poor: 75% H, found on disordered Follows after Pop 24.99% He, ~.01% elliptical orbits III; creating new metals; very gas poor pointing in all elements from H and (“red and dead”) directions; in the He… spheroid and in globular clusters; old stars Population I metal-rich: 70% H, ordered circular The generation of 28% He, ~2% orbits confined to stars today; metal- rich, have all the “metals”; gas-rich the galactic plane; on metals we know of. typically disk and in open clusters; young and old stars * Different stellar populations are understood in terms of the Chemical Evolution of Galaxies * metals are created by fusion deep inside massive stars (supernovae andAGB star winds enrich interstellar gas with metals) * each generation of stars forms out of gas enriched by previous generations * give clues to the formation history of the MWandAndromeda MilkyWay andAndromeda have supermassive Black Holes in their centers. Astronomy Final Study Guide 40 - found by effects of gravity on innermost stars — they orbit much faster than expected due to the intense gravity; given away by orbits of stars around them - also see excess x-ray and radio emission ** Use orbital speeds of stars to estimate the mass of the central black hole ** - The black hole at the center of the Milky Way is 4x10^6 the mass of the Sun - Andromeda’s black hole is nearly 100xs that of the MilkyWay ** Super large supermassive black holes are found at the center of all galaxies - Radius ~ 8 million km; the mass if 4x10^6 the mass of our Sun (roughly) - oddly, the Mass of a black hole has a ~.002 Mass bulge - Gregorian Relationship: black hole mass and galaxy bulge relationship ___ Galaxies, Clusters, and Superclusters Galaxies: - Basic units of luminous matter in the Universe - Building blocks of larger, organized structures - Primary sites of star formation from gas - powered by nucleosynthesis - Factories that synthesize heavy elements from H and He - *Differences among galaxies allude to differences in star formation histories and environments Astronomy Final Study Guide 41 * 3Types: * (all galaxies fall into 1 of the 3) - Spiral Galaxies (~75% of galaxies) - examples: MilkyWay andAndromeda - luminosity scales like stellar mass (close in number) - thin, rotating disks of stars, gas, and dust crossed by spiral arms - location of star formation and young, blue stars - made of older stars with little gas or dust — composed of old, evolved stars; no new stars being made at the time - central supermassive black holes with masses proportional to the bulge mass - bulge can range from big to small to none at all. - the bigger the bulge, the older the stellar population and larger central black hole; meaning the smaller the disk. - if there is no bulge…is there a black hole inside or not? - today, we can say there are not. Ablack hole cannot be detected, so the disk and galaxy can exist, but there’s no black hole. - Half of all spirals have a strong central Stellar Bar. - rotates as a unit (solid-body rotation) - spiral arms emerge from ends of the bar - looks like a wet football rolling tip-to-tip with water droplets coming off tips - bar is older than stellar population Astronomy Final Study Guide 42 - but short lived: spirals have the possibility of creating bars at some point, but will disappear - galaxies are very dynamic objects, and are always changing, which is why these bars come and go - Elliptical Galaxies (~20% of galaxies) - range from pretty normally sized to massive; diameter is much bigger than the largest spiral galaxies - have an enormous amount of globular clusters - little internal structure with little or no gas, dust, or star formation - have burnt up all gas to make all the stars it'll ever make; light of galaxy is dominated by light of giant stars (off-white color) - spheroidal (round but flat) - metal-rich evolved star population (brightest stars are giants) - most of gas, if any gas at all, is very hot - central supermassive black holes with masses proportional to the galaxy’s mass - can be really spherical or a flattened pancake. - Irregular Galaxies (~5% of galaxies) - chaotic, irregular structures and very gas rich; lumps - may have small disks or bars, but otherwise little ORDERED structure - may have formed the first stars in the galaxy - researched to find what the original metals of the galaxy were in the BB days - active star formation - many blue stars dominating their light Astronomy Final Study Guide 43 - very gas rich; up to 90% - some are among the most metal-poor galaxies (just now forming stars) - examples:The Large and Small Magellanic Clouds Most common galaxy (by number): Dwarf Galaxies *Tiny Ellipticals and Irregulars (no Dwarf Spirals) * Most often seen as satellites of larger galaxies * Most only contain a few thousand stars, and can be ~800 L of the sun - they are Distinct Objects — not just scaled-down ellipticals and irregulars - *may be extremely important…building blocks for how larger galaxies are settled? **Big galaxies are likely to run into other big galaxies a few times in their histories.** - Galaxies are only separated by ~20xs their diameters, leading to likely close encounters - 20:1 ratio of occurring - Star-to-star encounters are much more rare - Galaxies can interact and collide—boosting star formation, fueling central black holes, and causing transformative mergers (because of their gravities pulling each other together) - forming stars at a rapid, overwhelming rate upon collision; gas will be blasted away in only a few billion years **Andromeda is moving towards the Milky Way In a few billion years, we’ll merge and make an elliptical galaxy **Mergers play a key role in evolution** key to understanding how galaxies work Astronomy Final Study Guide 44 Galaxy organization (which formed first though?) Groups: 3-30 bright galaxies and many 10s of dwarfs Clusters: 30-300+ bright galaxies, and 100s to 1000s of dwarfs * Galaxies tend to group into Clusters * Many thousands of groups and clusters have been cataloged * 1-10 mega parsecs across in size, usually - the Local Group (our group) - group of ~50+ galaxies, includingAndromeda and the MilkyWay - the Virgo Cluster (nearest neighboring cluster) - nearest galaxy cluster to the Local Group - ~2500 galaxies with 2 bright Es (M84 and M87) - ~18 mpc away and ~2 mpc across - pretty small cluster **The richest clusters contain many thousands of bright galaxies—including rare giant Ellipticals - ellipticals founds near the center are red and dead - spirals found at the outer regions are forming stars - are the largest gravitationally-relaxed structures known - have the shape now that they’ll always have; no longer growing in mass * galaxies are relaxed, clusters are relaxed.. Superclusters - clusters of clusters - found along filaments that occupy ~10% of the Universe Voids - largest structures in the Universe Astronomy Final Study Guide 45 - outlined by filaments and walls - takes light billions of years to cross - place of virtually no galaxies - but how empty are they? **Existence of Large Scale Structure tells how galaxies are formed - sculpted by gravity - transient pattern - complex design; not just randomly distributed - concentrations of matter where galaxies formed ——— Scale of the Cosmos - remember — measuring distance for astronomical distances is v difficult. (THE MOST difficult thing to measure in astronomy) Astronomers use a distance ladder. - distances of planets are measured by AU (astronomical units) - average distance between Earth and Sun (as it’s constantly moving) is the “standard unit” of distance - distances of stars are measured by parsecs, or per 3.26 light-years First Rung of the Ladder: use radar to bounce radio pulses off of planets to measure distance * Inner Solar System (out to orbit of Jupiter): 10 AU diameter * Outer Solar System (out to Keiper Belt): 100AU diameter * Outer-outer-outer Solar System (out to orbit of Sedna): 1000AU diameter * about the edge of the Sun’s gravitational influence, or the edge of our Solar System Second Rung of the Ladder: measure distances to nearby stars with parallaxes (d = 1/p) Astronomy Final Study Guide 46 * within less than 7 parsecs, distance of nearest 100 stars * within less than 15 parsecs, distance of nearest solar neighborhood * within less than 75 parsecs, distance of the brightest 1630 stars * within less than 750 parsecs, is the distance of the OrionArm of the MilkyWay * structure of MW isn’t seen until out past >1000 parsecs out from Earth Third and Higher Rungs of the Ladder: * a standard candle is an object of known luminosity (absolute radiology) * simple in concept, difficult in practice * named from using lanterns to practice this idea * now we use a platinum blackbody (platinum at its melting point temperature) * if the luminosity is known (distance independent), and can measure apparent brightness, then distances is measured by the luminosity distance (print formula from lecture pls) Stars with similar spectra often have similar Luminosities - hot, blue, and luminous stars — upper-half end of spectrum - cool, red, and dim stars — lower-half end of spectrum Standard Candle: 1.Identify a distant star with a spectrum identical to the Sun’s (as an example) 2.Measure the star’s brightness, B 3.Assume the star’s luminosity, L — example, assume it’s the same as the Sun’s 4.Compute the star’s distance, d **The more luminous the standard candle, the greater the distance over which it can be used.** Examples of Standard Candles: - RR Lyrae stars: Milky Way and Local Group (stars that pulsate and are unstable) - Cepheid stars: Virgo and nearby clusters -Type Ia Supernovae: Superclusters and beyond **really good standard candle** - allow for looking at objects at billions of parsecs away Astronomy Final Study Guide 47 - solar systems = few AU - solar neighborhood = few parsecs - bright galaxies = 10s of kilo parsecs across (MWis 30 kilo parsecs in diameter) - at 300 kiloparsecs = MWand its satellite dwarf galaxies - at 3 megaparsecs = the Local Group (MW+Andromeda and all their satellites) - at 30 megaparsecs = clusters and groups of galaxies - everything in blue is a group, yellow is a cluster - structures are relaxed - 300 megaparsecs = superclusters (in blue) — long chains/walls of clusters parted by voids - structures are not relaxed—still in the process of forming - 3 gigaparsecs = it’s interesting; about where structure of the Universe maxes out (end of structure formation) - includes the Great Wall - shows that the Universe is NOT infinitely old… **On these scales, the force that rules is GRAVITY** Can get out to 28 gigaparsecs - which is the visible horizon of the Universe (as far as light can go; after this, the Universe becomes opaque to light) the further we go, the further back “in time” we go (light takes time to reach us… moon light to earth - 1 second (ie seeing the moon as it was 1 second ago) sun light to earth - 8 minutes pluto to earth - 6 hours Cosmic Look-back Time = key piece to observing the history of the Universe Astronomy Final Study Guide 48 ——- Showdown of the Centuries: Newton v Einstein **Newton and Einstein lived two centuries apart — meaning they lived in two completely different worlds with regard to understanding space, time, and gravity. - Fundamental physics => Newtonian - applications are now more modern, but the ideals have not changed for basic, applicable-to-everyday-life physics mg = mi for every known object at every location in the Universe. = Equivalence Principle ** gravity affects photon paths, even though they have no mass — they have energy, which has effective gravitational mass (m = E/c2) - Newtonian physics cannot explain this, but… - with Galileo -> two objects with different values of mg/mi fall at different speeds…but are they always? - Mg: If a box has a constant velocity, an apple will fall at a downward acceleration by gravity toward the center of the Earth - Mi: If the apple has that constant downward acceleration, but the box now is accelerating upward, it’s stuck in falling—hence the floating of people in space - Einstein went further—So, a beam of light follows a short, direct path between two points Astronomy Final Study Guide 49 - in a flat (Euclidean) space, as Newton believed in, the light would be seen as a straight line. - However, in the presence of gravity, the light path would be curved. **Therefore, in the presence of gravity, space is CURVED.** - but what is the “agency” that produces the force of gravity? there’s nothing physical holding them together. ? How does Earth’s mass know the Sun is there? ? Einstein’s view of gravity is really complex mathematically, but it works better than Newton’s when gravity is strong. - Strong meaning “near massive objects” Astronomy Final Study Guide 50 ** His theory correctly predicts gravitational lensing ** Gravitational Lensing: the effect of mass and energy causing space to curve, thus causing an observed bending of the path of light - proven by the first observation of the Sun during aTotal Solar Eclipse in May 1919 General Relativity is more accurate than Newtonian Gravity. In case that hasn’t been inferred yet. - accurately predicted amount that Mercury’s orbit precesses in arcsecond/century (Perihelion shift) -The effects of Einstein’s Theory of Relativity is essential to the functioning of the GPS satellite navigation system Type of Characteristics Interior Angle Parallel Light… Parallel Lines… Boundary or no Curvature Measurements Boundary? Euclidean (Flat) - two-dimen- equals 180 stays parallel never intersect no boundary tional space degrees (infinite) - flat universe - zero curvature Positive - Finite > 180 degrees converge eventually no boundary (but Spherical converge and has finite - High Density intersect volume) - spherical universe Negative - infinitely < 180 degrees diverge diverge and go has boundaries hyperbolic opposite ways you can fall off of - low density - “saddle” universe * matter tells spacetime how to curve; curved spacetime tells matter how to move Astronomy Final Study Guide 51 ——- Curved Space * Newton viewed space as flat and static (neither expanding nor contracting) * Einstein viewed space as curved and wavy, and it can expand or contract * different directions may require different paths to navigate *Matter tells space-time how to curve We perceive our world as in 3 dimensions — but space-time is 4 dimensions - visualizing this is extremely difficult - we have to resort to using 2 dimension analogies to illustrate the basic ideas of 4 dimension - requires really hard math * Under most circumstances, Newtonian gravity is good enough approximation and is computationally a great deal simpler Cosmological Principle: on large scales, the universe is homogeneous and isotropic - large scales = larger than superclusters (~100 Mpc) - homogeneous = same in all places; on scales bigger than stripe width - isotropic = same in all directions; around the central point, but at no other points ** homogeneity and isotropy ARE different — these are statistical statements *on small scales, the universe is not homogeneous *but on ~100 Mpc scales (large superclusters) the universe is statistically homogeneous at this size of perspective and above, we’re looking at the average, basically *the universe is also statistically isotropic on ~100 Mpc scales along any line of sight Astronomy Final Study Guide 52 Einstein’s General Relativity says that the curvature of space depends on the density of matter and energy - If the distribution of mass-energy is homogeneous and isotropic, then the curvature of space must also be homogeneous and isotropic. 3 ways of curvature under these conditions exist you use geometry to figure out which space you’re on when you can’t o


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