1ASTR 1040 ASTR 1040 AccelAccelAstroAstro::Stars & GalaxiesStars & GalaxiesProf. Prof. JuriJuriToomreToomreTA: Nicholas NelsonTA: Nicholas NelsonLecture 27 Tues 19 Apr 2011Lecture 27 Tues 19 Apr 2011zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomreSimulation: LargeSimulation: Large--scale structurescale structureTodayToday’’s `Cosmologicals `Cosmological’’EventsEvents••Discuss nature ofDiscuss nature ofdark matterdark matter••Look atLook atmodels for our universemodels for our universe, and what , and what prompted ideas about prompted ideas about bigbig--bangbangbeginningsbeginnings••Cosmic Microwave BackgroundCosmic Microwave Background••ReadRead22.3 22.3 Structure FormationStructure Formationand and 22.4 22.4 Fate of UniverseFate of Universein detailin detail••Overview read Overview read ChapChap2323Beginning of TimeBeginning of Time••New New Homework Set #12Homework Set #12passed outpassed outHow much How much dark matterdark matteroverall?overall?••All galaxy cluster methods generally agreeAll galaxy cluster methods generally agree••About About 10 times as much dark matter10 times as much dark matteras as ““normalnormal””mattermatteroverall in the universeoverall in the universe••Note: Our solar system has much more light Note: Our solar system has much more light matter than dark matter here! (DM probably notmatter than dark matter here! (DM probably notmeasurable measurable ––why sowhy so?)?)What is Dark Matter?What is Dark Matter?••Two flavors for Dark MatterTwo flavors for Dark Matter::••Possibility 1.Possibility 1.MACHOsMACHOs••Massive Compact Halo ObjectsMassive Compact Halo Objects••Stuff weStuff we’’ve studied already: very faint, actual ve studied already: very faint, actual things; baryonic matterthings; baryonic matter••Brown dwarfs, black holes, black dwarfs Brown dwarfs, black holes, black dwarfs ……etc.etc.••May be floating through the galaxy halo unnoticedMay be floating through the galaxy halo unnoticedPossibility 2.Possibility 2.WIMPsWIMPs••Weakly Interacting Massive ParticlesWeakly Interacting Massive Particles••NonNon--baryonic baryonic subatomic particlesubatomic particle••Neutrinos? probably notNeutrinos? probably not……. they move too fast . they move too fast and cannot be collected into stable galaxy halosand cannot be collected into stable galaxy halosOther unknown particles ???Other unknown particles ???Slower particles: Slower particles: ““Cold Dark MatterCold Dark Matter””MACHO SearchesMACHO Searches••Use gravitational Use gravitational lensinglensing••When a MACHO When a MACHO floats in front of a floats in front of a star, the star, the star star suddenly suddenly brightensbrightens••Focusing effect Focusing effect of compact of compact massive objectmassive objectMACHOMACHOSTARSTAROBSERVEROBSERVER2MACHO huntMACHO huntresultsresults••MACHOsMACHOsare are detected by detected by brighteningsbrightenings••But not But not enough to enough to explain all explain all dark matterdark matterReading clicker: gravitational lensReading clicker: gravitational lens••If you measure the If you measure the redshiftsredshiftsof the of the yellowish and blue yellowish and blue objects, youobjects, you’’ll find:ll find:A.A.The yellow galaxies have The yellow galaxies have similar redshifts, all higher similar redshifts, all higher than the blue galaxiesthan the blue galaxiesB.B.The blue galaxies have The blue galaxies have the same the same redshiftredshift, which is , which is higher than the yellow higher than the yellow galaxiesgalaxiesC.C.Yellow and blue galaxies Yellow and blue galaxies have similar redshiftshave similar redshiftsB.B.LensingLensing••B.B.The blue The blue images are a single images are a single BACKGROUND BACKGROUND galaxy being galaxy being lensedlensedby the foreground by the foreground cluster (yellow cluster (yellow galaxies)galaxies)••The blue galaxy is The blue galaxy is farther from us and farther from us and thus will have a thus will have a higher higher redshiftredshiftModels of ourModels of ouruniverseuniverseDark matter hasDark matter hasbig influence onbig influence on““openopen””vsvs““closedclosed””If enough mass, gravity eventually wins!If enough mass, gravity eventually wins!Predictions of General Relativity Theory (GRTPredictions of General Relativity Theory (GRT))••EinsteinEinsteinin 1917 realized GRT predicted universes in 1917 realized GRT predicted universes in motionin motion, but preferred `steady state, but preferred `steady state’’––added added `cosmological constant`cosmological constant’’(CC) as repulsive force in (CC) as repulsive force in spacespace--time to counteract attractive force of gravitytime to counteract attractive force of gravity••Willem de SitterWillem de Sitter(A, Dutch, 1917)(A, Dutch, 1917)solves GRT solves GRT equations with no CC and low density of matter : equations with no CC and low density of matter : showed universe must expandshowed universe must expand••Alexander Alexander FriedmannFriedmann(M, Russian, 1920)(M, Russian, 1920)solves solves GRT with no CC but any density of matter : GRT with no CC but any density of matter : universes can expand forever, or collapse again,universes can expand forever, or collapse again,depending on mean matter densitydepending on mean matter densityEARLY DEVELOPMENTSEARLY DEVELOPMENTSMore on More on ……Predictions of GRTPredictions of GRT••Georges LemaitreGeorges Lemaitre(P, Belgian, 1927)(P, Belgian, 1927)rediscovers rediscovers FriedmannFriedmannsolutions, told solutions, told Hubble Hubble (observing (observing redshiftsredshiftssince 1924) that since 1924) that cosmic expansioncosmic expansionsuggests more distant galaxies should have greater suggests more distant galaxies should have greater redshiftsredshifts(Hubble publishes V = H(Hubble publishes V = Hood in 1929)d in 1929)••Einstein visited Hubble in 1932Einstein visited Hubble in 1932,,said CC said CC ““biggest biggest blunderblunder””3Various Various FriedmannFriedmannGRT solutionsGRT solutionsOld language: Old language: Open, Marginally Open, Closed, OscillatingOpen, Marginally Open, Closed, OscillatingNew: Accelerating, Coasting, Critical, New: Accelerating, Coasting, Critical,