AST207 F2010 12/1/20101Ast 207 F2010Universe at 400,000yr—1 Dec• Cosmic background radiation is a snapshot of U at 400,000 yr.• What is in the snapshot?– History of MW & local group: motion of 300km/s– Fluctuations at an angular scale of 1.– Growing clumps of mass mass density of the universe– Evidence of first starsTemperature of radiationfrom Big Bang,measured by WMAP satelliteUniverse at 13.7Byr & 11.7Byr• M101 is a snapshot of the universe.– v=1050km/s– D=v/H=1050/60=18Mpc=18*3.2=56MillionLight year– Light took 18Myr to get to us.1. Light from Abell2218 took 2Byr to get to us. Are all of the objects in the picture of Abell 2218 from the time when the universe was 11.7Byr old?A. YB. NAst 207 F2010M104Abell2218AST207 F2010 12/1/20102Universe at 4min• At 3min– Neutrons got incorporated into 4He.– Temperature was 1BK.1. If you could go back in time to when the U was 4min old and take a picture, what would you see? Stars. Very hot black‐body r adiation.A. S and VB. S onlyC. V onlyD. Neither S nor V.Ast 207 F2010Universe at 4min• At 4min, U was slightly cooler than 1BK.• There were no stars, no galaxies, no planets. These could not form when the temperature was so hot.Ast 207 F2010AST207 F2010 12/1/20103Ast 207 F2010Ionized/un‐ionized gas• Ionization is the loss of an electron.H atom p + e‐• Recombination is when electron and nucleus combine.p + e‐ H atom• Ionization occurs if the temperature is hot enough.1. Name one thing in this room that is/has ionized gas.A. Gas in fluorescent lightB. AirC. Air in my lungs• Light scatters poorly off of electrons bound in an atom or molecule.• Light scatters readily off of free electrons.photonelectronAst 207 F2010• If the air were ionized, light would travel 500m before it is scattered. Light scatters nearly equally in all directions.1. If the air were ionized, could you, sitting in Michigan Stadium, watch the Spartans beating Michigan? Could you see stars at night?A. YYB. YNC. NYD. NN• If the air were ionized, the air would be a fog.• We do not have a picture of the U at 4min, because at such a high temperature, the U is ionized. Light could travel only a short distance before scattering of an electron.photonelectronAST207 F2010 12/1/20104Ast 207 F2010Matter and Radiat ion Decoupled• Early, hot universe– Hydrogen is ionized.• Protons and electrons are free– Universe is opaque.• Photons travel only short distances.• Scattered by free electrons.• Decoupling: p + e‐ H atom– T = 3000 K; universe 400,000 yr old.– Universe becomes transparent• Photons decouple from matter, continue in whatever direction they were moving.• After decoupling– Photons travel in same direction. Preserves information about the matter at decoupling.– In certain directions, matter & light were slightly more dense. Light preserves that information.photonelectronBefo re & after decoupling• Adam was sent back in time to when the U was 300,000yr old. Noah was sent back to when the U was 500,000yr old. A & N sent us a message that they are toasty warm.1. Can we get their messages?A. Y for bothB. Y for A, N for NC. N for A, Y for ND. N for both.Ast 207 F2010AST207 F2010 12/1/20105Ast 207 F2010EarthTransparentUniverseOpaqueUniverseOpaqueUniverse13.7 billionlight yearsA Snapshot in TimeDenser hereRadiationhotterAst 207 F2010Wilkinson Microwave Anisotropy Probe (WMAP) Satellite• Goal: Take a picture of the U when it was 400,000yr old.– Measure spatial variations in temperature of the CBR.• Measure anisotropy– Penzias & Wilson found radiation to be isotropic.– Goal is to measure small deviations.• Sensitivity is 0.000035K (a part in 100,000).• Anything in the instrument even 0.0001K warmer is fatal.• Symmetric design– Record temperature difference between left & right channels. Temperature difference is small.– Rotate entire instrument.• Instrumental problems do not change; radiation from the sky does change.AST207 F2010 12/1/20106Ast 207 F2010Wilkinson Microwave Anisotropy Probe (WMAP) SatelliteDave’s notebook 3/20/1991, Greg TuckerDave Wilkinson1935-2002, b. Hillsdale MIAst 207 F201010 microwave eyes on right10 microwave eyes on leftAST207 F2010 12/1/20107Ast 207 F2010Local Motion• WMAP: Temperature of CBR across whole sky• Notice Milky Way (pink)• Earth, sun, MW, & local group of galaxies move at 300 km/s with respect to whole universe.1. The earth, sun, and Milky Way are moving toward which direction? In which direction is wavelength compressed?adcb2.732 K2.724 KAst 207 F2010Remove motion• Remove motion and show with increased contrast• Largest fluctuations are at an angular scale of 1º.Temperature fluctuations:Light & dark
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