ASTR 1120General Astronomy:Stars & Galaxies• FINAL: Saturday, Dec 12th, 7:30pm, HERE• ALTERNATE FINAL: Monday, Dec 7th, 5:30pmin Muenzinger E131• Last OBSERVING session, Tue, Dec.8th, 7pm• Please check your grade on clickers, midterms,HWs on CU learn - e-mail Thomas if you seediscrepancies/missing grades• Homework #9 due TODAY, by 5pmOUR Universe:Accelerating Universe• Dark Energy iscausing theexpansion ofthe universe tospeed up overtime!• Scientists don’tknow what thisdark energymight be.REVIEW Chapter 23: In the VERY BeginningBIG BANG: beginning of TimeEarly times in the Universe were reallyHot Stuff!!• If the universe is coolingand expanding now…– The Universe was hotter atearlier times• The temperature at theearliest times was morethan the energy we createin even our largest particleaccelerators• Cosmology at the earliesttimes is explored viaparticle physicsPhotons converted intoparticle-antiparticlepairs and vice-versa(Matter and Energy arethe same!!) E = mc2Early universe was fullof particles andradiation because of itshigh temperatureMatter, Antimatter, and EnergyPlanck Era0 - 10-43 secBeforePlanck time=???•Things wereso small andso dense…modernphysics fails–No theoryof quantumgravity• Gravity• Electromagnetism• Strong Force• Weak ForceThe Four KnownForces in the UniverseFour known forcesin the universe:• Gravity• Electromagnetism• Strong Force• Weak ForceDo forces unify athigh temperatures?Four known forcesin the universe:• Gravity• Electromagnetism• Strong Force• Weak ForceYes!(Electroweak)Do forces unify athigh temperatures?Four known forcesin the universe:• Gravity• Electromagnetism• Strong Force• Weak ForceYes!(Electroweak)Maybe (Grand Unified Theories)Do forces unify athigh temperatures?Four known forcesin the universe:• Gravity• Electromagnetism• Strong Force• Weak ForceYes!(Electroweak)Maybe (GUT)Who knows?(String Theory)Do forces unify athigh temperatures?GUT Era~10-43-10-38 secLasts fromPlanck time toend of GUTforceInflation of the Universe• As strong forcebecomes distinct (endof GUT era), a hugeamount of energy isreleased• Universe INFLATES:– Universe of atomicnucleus size becomessolar system size in10-36 secElectroweakEra~10-38-10-10 secLasts from end ofGUT force to endof electroweakforce•Universe stillmade up ofelementaryparticles (quarks)Particle Era(10-10-.001 sec)Finallytemperatures lowenough thatquarks cancombine to formsubatomicparticles (protons,antiprotons,neutrons,antineutrons,etc…)The ParticleEra• Universe still hot: 1015 to1012 K• Particles now exist:electrons, protons, anti-protons, anti-electrons,neutrinos etc.• Particle soup! Particlesand photons/energycreated and annihilatedAt the end of the particle era, temperatures are lowenough that photons cannot collide to creatematter/anti-matter anymore. Nearly all the matter andantimatter that is in the universe at that time collidesand forms photons. But a little bit of some type ofmatter remains… which type is it?A. Regular matterB. Anti-matterC. There’s no way wecan tell!Clicker QuestionAt the end of the particle era, temperatures are lowenough that photons cannot collide to creatematter/anti-matter anymore. Nearly all the matter andantimatter that is in the universe at that time collidesand forms photons. But a little bit of some type ofmatter remains… which type is it?A. Regular matterB. Anti-matterC. There’s no way wecan tell!Clicker QuestionMatter and Anti-matter• At end of particle era,universe contains matter!• Protons must haveslightly outnumbered anti-protons• Universe ratio today:– 1 billion photons (light) forevery 1 proton (matter)• Universe ratio then:– 1 billion and 1 protons forevery 1 billion anti-protonsEra of Nucleo-synthesis0.001 sec-3 minBegins whenmatter annihilatesremainingantimatterEra of Nucleosynthesis(Fusion)• Matter particles are“frozen out”– no longerspontaneouslygenerated to/fromphotons• Temperatures hotenough to fuseprotons (hydrogennuclei) into heliumnucleiNucleosynthesis stops afterabout 3 minutes• Fusion ends because density drops– remember the universe has been expanding thiswhole time– Matter left as ~75% hydrogen, ~25% helium, withtrace amounts of lithium, deuterium• Amounts seen throughout the universe today(with slight enhancements of heavy elementsfrom fusion in stars)Era of Nuclei3 min -380,000 yrs•Most matter wasin the shape ofhydrogen/heliumnuclei, electrons•Universe hasbecome too coolto blast heliumapart but too hotto allow electronsto combine withnuclei to makeatomsThe era of nuclei created a lot oflight but it couldn’t get anywhere!!• Density was sohigh, photonswould hit anelectron or nucleibefore gettinganywhere– Just like therandom walkinside the Sun!380,000 yearsto 1 billionyears•Finally, thetemperaturedrops to about3000 K andelectrons allcombine withnuclei to formthe first atomsEra of AtomsEra of Atoms• Finally cool enough(3000 K) for electronscombine with nucleito form atoms(380,000 yrs)• Photons now“decoupled” = freeto fly away• Universe becomestransparent to lightEra of Galaxies1 billion years -nowEra of Galaxies• About 1 billion years after Big Bang, first starsand galaxies start to form• We live in the Era of Galaxies now.Big Bang evidencePenzias & Wilson in 1965discovered Cosmic MicrowaveBackground (CMB) radiation --> 2.73 K “black body”Photons created when hot universe was only 380,000 yrsold – as first atoms formedVery uniform radiationfrom everywhere – 1 part in 100,000 severely redshifted byexpansion of universeWMAP1978 Nobel Prize Spectrum of Cosmic Microwave Background (CMB)2.73 K `black body’Light from beginning of time• This faint light looks light a solid glowing wall• Thermal spectrum at 3000 K, if redshifted by factor~1000 ! microwaves!• Helps measure degree of isotropy in earlyUniverseChemical abundances alsoconfirm the Big Bang model• Big Bang Theoryprediction: 7-1proton-to-neutronratio– Should lead to75% H, 25% He(by mass)• Matchesobservations ofnearly primordialgasWhich of these abundancepatterns (by mass) is anunrealistic chemical compositionfor a star?A. 70% H, 28% He, 2% otherB. 95% H, 5% He, less than 0.02% otherC. 75% H, 25% He, less than 0.02% otherD. 72% H, 27% He, 1% otherClicker QuestionWhich of these abundancepatterns (by mass) is anunrealistic chemical compositionfor a star?A. 70% H, 28% He, 2% otherB. 95% H, 5% He, less than 0.02%