Survey of Astronomy
Survey of Astronomy ASTR 1050
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This 64 page Class Notes was uploaded by Kobe Funk on Tuesday October 27, 2015. The Class Notes belongs to ASTR 1050 at University of Wyoming taught by Sabrina Cales in Fall. Since its upload, it has received 19 views. For similar materials see /class/230338/astr-1050-university-of-wyoming in Astronomy at University of Wyoming.
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Date Created: 10/27/15
I Welcome toAstron0my1950 39 Pleas cgme and get a syllabus and a sheet 01 mm pagief 0quot me side nSLhe she39 39nfpzyq please pll 1 Ynllr name mainr year in39scimnnl 39 mh39arrzssed irI39 fiwntimged in clz39ss 3 D eming Abnqm zs39sunnnm thztyyu areclu Mr Daniel Kiminki preferably just Dan quot h Course ugstions What s up there How does it work How do we Mow We won t be just exploring Astronomy but Astronomy as a science as well Textbook WebCT occasionally a calculator and your imagination Qf 39 Chapter391z 1 TQe Scale of the Cosmos 4 Astronomy39dealswi th on vast range 39 pf size scaIeS a39ndtimescales Mdst offhe e size and39time 39s39cales39 re 39way beyond ouf ev39erydayexperi39ehce39 39 4 Humansftm iEarth arid even the so lar system are tiny on cosmic scaIwQuestion does tiny imply unim on ant A Campus Scene a 2m amwcn39a Yhnmsan 16x16m A City View a 2005 Blmkslcole Thcmscn a 2006 Bmwoaie rTnalrson 1 mile x1 mile 16 km x 16 km The Landscape of Pennsylvania 2005 amencow Thomsan 100 miles x 100 miles 160 km x 160 km Visualwavelength image is 2W5 Bmks coie r Tnuusnn 2006 Etwlslcok Thmnsan Diameter of the Earth 12756 km amd Mm 1 391 ll l l Enlarged to show relative size Visualwavelength image c 2005 Eyaakscale Thurman Earth Moon g ame Ea h W mzrn 349 km f4 zous E mowcme Thwsnn Earth orbiting around the Sun Distance Sun Earth 150000000 km Earth orbiting around the Sun In order to avoid large numbers beyond our imagination we introduce new units 1 Astronomical Unit AU Distance Sun Earth 150 million km ems EmuCal mmn The Solar System Pluto in January 1979 Jupiter Saturn Pluto in March 1999 2m BrmksJCoie v Thomson Mercury Enlarged to show relative size macs Ernakscn a v Thomson Approx 100 AU Almost Empty Space Around our Solar System Approx 10000 AU The Solar Neighborhood 2005 swankThomquot Mme anxstcm Thumsm Approx 1739 light years The Solar Neighborhood New distance scale 1 light year Iy Distance traveled by light in 1 year 63000 AU 1013 km 10000000000000 km 1 13 zeros 10 trillion km Nearest star to the Sun man Proxima Centauri at a distance of Approx 17 light years 42 light years Th Extgmdgd SH quoth WQ 39 031 39 jsda lVTavelerigh g399 39 39 E To II Appmxa ght Wang Thg M y Wy Ga axy Visualwavelength image r9 2006 Evoaks ca e Thansun ammcgr f cm Mi ky y w 759C y Milky Way Galaxy 3 4 Visualwavelength image a 2m magnum J39mmsm 2006 avwxs39CoIe gtThomsun gimme m Em neamg arm gal axies gemm minim gm yaafg The Universe on Very Large Scales Milky Way Galaxy gt39 d innus Blanks in 20115 Broaks Caia Whaman Clusters of galaxies are grouped into superclusters Superclusters form filaments and walls around voids A word from the Guide The simple truth is that interstellar distances Will not fit into the human imagination Douglas Adams Therefore we re going to need to use some large numbers Useful Units See Appendix of textbook and notes from lecture Small break Based on what you know about the Hubble Law from last time if galaxy B is 5 times farther away than galaxy A A The velocity of galaxy B is 5 times larger B The velocity of galaxy B is 25 times larger C The velocity of galaxy A is 5 times larger D The velocity of galaxy A is 25 times larger vBHOdB 12 3 dB 5 VAHOdA VA dA 1 7 7quot by Mark Pansi a m a I k c o m c z s maksrco ermnmsan Ancient view from the Greeks Aristotle until the 1970s the universe was infinite and unchanging Modern cosmology has changed that view by showing that 1 The universe is expanding 2 The universe contains left over glow of radiation the Cosmic Microwave Background radiation from an initial explosion 3 The night sky is dark 4 The oldest star clusters have ages of 1214 Gyr This depends on the stellar model used to estimate the age of the turn off stars Olbers s Paradox Why is the sky dark at night Ifthe universe is infinite then every line of sight should end on the surface of a star at some point gt The night sky should be as bright as the surface of stars Solution to Olbers s Paradox If the universe had a beginning then we can only see light from galaxies that has had time to travel to us since the beginning of the universe gt The visible universe is finite Red Shifts 1200 kms giant ga mx gg are 15000kms rgggdmg fmm US with a Sp d L U p i a d gtgmc 22000 kms A1000 39 1 5 3 m if E Q39 4 g 11 go gt 61000k 0 Hydra m S x Unshi ed position 0 o of calcium lines 0 1 2 Distance MDC The Expanding Universe On large scales galaxies are moving apart with velocity proportional to distance It s not galaxies moving through space Space is expanding carrying the galaxies along quot Vquoti 39 I U x w 4 3quot N Iquot quot I r L l x x IN 5 a The galaxies themselves are not expanding Expanding Space Analogy A loaf of raisin bread where the dough is rising and expanding taking the raisins with it The Expehdthg Uhhtt e Ht Thte deee het meeh thet we ere at the eehtet et the Uhtvereet Yew heve the eeh te tmpteeeteh treht ehy ether ge exy ee went a F es fa Kg l 55quot i9quot Knewing the current rate at expansien at the universe we can estimate quothe time it teak fer 39 te nieve as tar apart as they are tenay gaiaxres Time a distance weieeity traineity H0 distance distance distance 1 velocity H0 x distance H0 km 1 T x308x1013 km x106 70S C Mp5 44x1017s 14x1010 yr 14Gyr Enter an answer in billions of years Light we see teday iett this gaiaxy when the universe was eniy i hiiiien years eieil I Visual infrared image If the Hubble Constant were 140 kmsMpc 003 instead of 70 the implied age of the universe would be Twice as large Four times as large 12 as large 14 as large Showing the Hubble Law expansion using a bunge distance D1 D0 V time 1s Galaxy DistanceO Distance1 Velocity MW NGC1OO 30 53 23 NGC10030286 30 53 23 MW 30286 60 110 50 MW PK8031 2 120 166 76 1 Lee e m Beek Tewerde i 35 m n the Umveree quot 39 GA ti J 52 The mere dietem the ebjecte we ebeerve the fu iher beck irate the pest ef the universe we are eekmg I 39 I if 1 39 39 39 quot 539 9 l Ifquot I H 39 SIAAquot g 39 39 quot A 7 Amee zs 6 2005 B39uoksfcwe Tnomsun The Cosmic Background Radiation The radiation from the very early phase of the universe should still be detectable today Was discovered in mid1960s as V the Cosmic Microwave Background 39 FE Wilso ampA Pezis Radiation Black body radiation with a temperature of T 273 K T 2725 r 0002 K Intensity 39 005 01 05 1 Wavelength cm Universe cools down as time passes The History of the Universe Radiaiion dominates Matter dominates 1010 108 Temperature K 8 5 a m 103 Time 2005 mummy Tllumsun Universe expands as time passes The Early History of the Universe 0 Electron 0 5 lt5 0 Positron W AN Gammaray photon O I 1 Radiation Matter i010 dominates dominates we jg Electrons positrons and gamma A m g rays In equnllbrium between pair 9 105 Formation of E g elements g production and annihilation e o l 4 E 10 Now 102 Cooling in the bigbang universe V 1 Formatlon of galaxies I l I l l is 1min 1h lday iy lOzy i04y i06y iOBy lOmy Time The Early History of the Universe ll Protons and neutrons form a few 25 Of mass in helium helium nuclei the rest of protons 75 in hydrogen remain as hydrogen nuclei I J No stable 939 ergr liqlinn 1 10 dom n t c Iquot 39 10 I I aes i With 5 8 I m7L1 I 108 I protonS Bu Q g i To 106 Formation of l i 3 elements I 4He 9 I p D 3He 3 104 l 3 2H I 2 iH 10 Cooling in the E bigbang universe I FormatIon of gamm 9 Almost no I I I I I I I ii I I eements heavier is 1min Ih lday iy 102y Io4y 106 way 101 than helium are produced Time Temperature K The Early History of the Universe lll Photons are incessantly scattered by free electrons photons are in equilibrium with matter R 1010 Radiation dominw V f i 108 X quotl Formation of El 106 elements 8i w I Radiation dominated era 102 1 Cooling in the i bigbang universe 3 l I l iOGy is 1min 1h 1day ly iOZy io4y Time Formation of galaxies Photons have a black body spectrum at the same temperature as matter atter dominates Now iOSy lOmy i ornperz iture K Recombination Dense ionized gas Protons and electrons recombine to form atoms gt Universe becomes transparent for photons z 1000 Radiation Lowdensity ionized gas I 7 to dominates dominates g l H l El 103 i ormation oi E elements St a toquot TranSItion to matter I dominated era 3 A i m Cooling in the bigbang universe 1 1 Formation of galaxies i l l l I l i a i min 1 n i day i y 39lOZy toty toby 10 10 Time Temperature K The Cosmic Background Radiation After recombination photons can travel freely through space Their wavelength is only stretched redshifted by cosmic expansion Radiation Matter dominates dominates 10539 106 Formation oi E elements 8 4 Recombination amp 10 Ozz 1000 T 3000 K Cooling in the bigbang universe Formation of galaxies l i is imin 1h lday ly roiy i04y TOGy rosy TOmy Time This is what we can observe today as the A distant galaxy emits a short wavelength photon toward our galaxy v The expansion of spacetime stretches the photon to longer wavelength as it travels The farther the photon 5 i has to travel the more it is stretched When the photon arrives at our galaxy you see it with a longer wavelength a redshift that is proportional to distance 2006 Eronklenle Thu cosmic background radiation Reionization After less than 1 billion years the first stars form Ultraviolet radiation from the first stars reionizes gas in the early universe Radiation Matter 10 dominates VE dominates V 108 a I Q E39 V Di 9 106 Formation of E elements g cm Sci 104 Formation of the i a first stars Reionization 2 0 Cooling in the big bang universe a uanerse 1 Formation if gallaxies becomes I I I I I I I I I I I O a l s 1 min i h lday 1 y lOZy to4y io 5y lOSy lOIOy p again So where did the big bang come from Classical answer is that time itself also came into being then so we can t really ask what came before And for that matter 1 Why do we live in a universe which is finely balanced between expansion and contraction flatness problem Gravity could cause a slow down and collapse or the universe could expand so fast that galaxies and stars never formbut it didn t 2 Why do we live in a universe where gravity and nuclear forces are balanced such that stars can shine and produce energy for billions of years 3 Why do we live in a universe where nuclear energies inside He and C and other atoms are arranged such that heavy elements can be made at all These are examples of finetunings in nature Broad categories of answers 1 These fine tunings are a consequence of some more fundamental law of physics that we don t yet know 2 There are a great many perhaps infinite number of universes and ours just by chance happens to be one where things worked out right or we would not be here asking this question 3 The universe is a purposeful work of a transcendent agent ie God outside of space and time Astronomers and Physicists hold a wide range of personal opinions spanning the above The Cosmological Principle Considering the largest scales in the universe we make the following fundamental assumptions 1 Homogeneity On the largest scales the local universe has the same physical properties throughout the universe Every region has the same physical properties mass density expansion rate visible vs dark matter etc 2 lsotropy On the largest scales the local universe looks the same in any direction that one observes You should see the same large scale structure in any direction 3 Universality The laws of physics are the same everywhere in the universe Cosmology and General Relativity According to the theory of general relativity gravity is caused by the curvature of spacetime The effects of gravity on the largest cosmological scales should be related to the curvature of spacetime The curvature of spacetime in turn is determined by the distribution of mass and energy in the universe Spacetime tells matter how to move matter tells spacetime how to curve a mm mm Cole mummy a am y Shape and Geometry of the Universe Back to our 2dimensional analogy How can a 2D creature investigate the geometry of the sphere Measure curvature of its space 92m Broom cuie Pub Closed surface Flat surface surface positive curvature zero curvature negative curvature Deceleration of the Universe Expansion of the universe should be slowed down by mutual gravitational attraction of the galaxies Fate of the universe depends on the matter density in the universe Define critical density pc which is just enough to slow the cosmic expansion to a halt at infinity Size scale of the universe Model Universes Maximum age of the universe 1H0 p lt pc gt universe will expand forever to e 7Fa UnNefs Closed p gt pc gt universe will collapse back 14 95 H Billion years ago NOW Past Future gt Time Time lfthe density of matter equaled the critical density then the curvature of spacetime by the matter would bejust so sufficient to make the geometry of the universe flat Dark Matter Combined mass ofall visible matter ie emitting any kind of radiation in the universe adds up to much less than the critical density v Gravitational lensing shows that some clusters contain 10 times as much mass as directly visible The Nature of Dark Matter Can dark matter be composed of normal matter Deuterium K Deuterium abundance falls in this range Abundance a Lithium 7 abundance falls in this range I Lower limit on density 39 Upper39limit on density l Ausqu leouuo Lithium77 1 Density of normal matter l 5 10 If so then its mass would mostly come from protons and neutrons baryons The density of baryons right after the big bang leaves a unique imprint in the abundances of deuterium and lithium Density of baryonic matter is only 4 of critical density milli ihark matter must be nonbaryonic exotic particles Mr Spock cleanse the baryons from our hull If the Hubble constant were 50 kasMpc instead of 72 kmsIMpc what would the age of the universe be Hi309x1013 kmpc106 pcMpc 0 HIGXIO19 kmMpc 7750 50 72 13x1019 kmMpc Problems with the Classical Decelerating Universe 1 The flatness problem The universe seems to be nearly flat Even a tiny deviation from perfect flatness at the time of the Big Bang should have been amplified to a huge deviation today gt Extreme fine tuning required 2 The isotropy of the cosmic background If information can only travel through the universe at the speed of light then structure in the cosmic background should not be correlated over large angular scales 2 Contradiction to almost perfect isotropy of the cosmic background Measuring the acceleration ot the Universe y observing type la supernovae astronomers can measure the Hubble relation at large distances Hos galaxy Supernova 29 March 1997 5 April 1997 Distance 6 recession speed Size scale ofthe universe 9 rate of expansion lt was expected that this would measure the deceleration otthe universe but Apparent Magnitude of The Accelerating Universe Type a Supernovae 19 N 20 a Fiat decelerating universe a S 21 I 5 Flat accelerating un verse E a 22 n I E E 9 23 i O 24 Observations of type Ia supernova fit an accelerating universe but not a decelerating universe 25 01 02 04 16 1 0 Redshift z mmmmmmmmmmmmmm unison Red Shift Z In fact SN a measurements showed that the universe is accelerating 21St Century Cosmology The solution Inflation 1 043 l 1035 Age of universe seconds inflation Electroweak force toquot Gravitational force l Electro magnetic force Weak force Strong force l 1 o32 1027 1015 Inflation period of sudden expansion during the very early evolution of the universe triggered by the sudden energy release from the decoupling of the strong and electroweak forces Temperature K The Evolution and Ultimate Fate of the Universe Xray images Until 6 billion years ago gravity of matter was stronger I Scale of the universe than acceleration Big bang Big rip Constant 67 billion ly dark energy Today 35 bllllcn ly acceleration cl u e to da rk mew e n e rgy do minates Dark energy overcame gravity and acceleration began about 6 bl lion 1 billion ly years ago Future Present Time 6 2n mmmmmmmmm l5 mrum Let s summarize Our best current estimate is that the universe is 1 Flat 2 Open 4 CIOSEd 18128137 8 Accelerating 16 Decelerating 32 Dominated by baryonic matter 64 Dominated by radiation 128 Dominated by dark matter 256 Most of the dark matter is baryonic Add together the true statements and enter The Cosmological Constant Cosmic acceleration can be explained with the cosmological constant A Lambda A is a free parameter in Einstein s fundamental equation of general relativity previously believed to be 0 Energy corresponding to A can account for the missing massenergy E mc2 needed to produce a flat spacetime a dark energy SWUGWWQ Disiribiiiion vii brigi ii gaiaxies ii i iiie Virga regiOri irioiicaries 39ii39ie Virgo CiiiS39ier arid presence 0i merre disgrarii iarger scaie S39iriiciiire LargeScale Structure II A large survey of distant galaxies shows the largest structures in the universe 39 Filaments and walls of galaxy superclusters and voids basically empty space Cosmology with the Cosmic Microwave Background If the universe was perfectly homogeneous on all scales at the time of reionization z 1000 then the CMB should be perfectly isotropic over the sky Instead it shows smallscale fluctuations Fluctuations in the Cosmic Microwave Background Angular size of the CMB fluctuations allows us to probe the geometry of spacetime CMB fluctuations have a characteristic size of 1 degree Analysis of the Cosmic Background Fluctuations Common Open un verse Occurrence Flat universe was Rare Analyze frequency of occurrence of fluctuations on a particular angular scale gt Universe has a flat geometry l l t E E 4 Angular size degrees mi Based on the fact that the universe is mostly hydrogen 1 6x103927 kg per atom and that the sun s mass is 2x1030 kg use a rough guess for the number of stars in the Milky Way to estimate the number of hydrogen atoms in our galaxy Enter the exponent of this number 1011 t 2 1030 quot g 1 Eng 23 kg SW 125x1068at0ms x atom What kinds of checks and tests do we have on the standard big bang cosmology 1 Predicts CMB radiation which is observed at about the right temperature 2 Predicts mostly H and He formed observations of dwarf galaxies and very old lowmass stars plus observations of gas at high redshifts z5 confirm few metals are present at early times 3 Gravitational lensing allows us to measure masses of clusters largest structures agree with expectations of cosmology