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Primordial Sound: Listening to the Big Bang

Primordial Sound: Listening to the Big Bang

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Primordial Sound: Listening to the Big Bang

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  1. Primordial Sound: Listening to the Big Bang Mark Whittle University of Virginia

  2. Outline • Our Universe & the Big Bang • The Microwave Background • Sound in the early universe • The birth of the first stars and galaxies • In the beginning: quantum hiss

  3. The Sun: A Normal Star

  4. Solar magnetic surface storm

  5. Jewel Box Cluster Naked eye stars Eagle Nebula Crab Nebula Our Galaxy Earth = 100 nm = virus Sun = 10 μm = cell Earth orbit = ¼ cm = pin head Solar system = 20 cm = saucer Nearest star = 250 m = canteen Solar system Galaxy Center

  6. Galaxies are BIG They contain 100,000,000,000 stars! A hundred thousand million

  7. NGC 891 edge on Spiral Galaxy

  8. 2 million galaxies in a patch of sky

  9. The Sloan and 2DF galaxy surveys

  10. SDSS : ⅓ million galaxies Doppler shifts give galaxy velocities 3 billion light years (~20% to “the edge”) Our galaxy is here

  11. The Universe is EXPANDING

  12. View from galaxy A B A

  13. View from galaxy B B A

  14. Expansion started at one moment, about 14 billion years ago. We call this: The Big Bang!

  15. Witnessing History

  16. Telescopes are also Time Machines

  17. Hubble Deep Field Small, un-remarkable region: 1500 galaxies! HST image HDF

  18. Far away, galaxies appear younger

  19. SDSS & 2dFGRS HDF “Nearby” galaxies 13.7 Gly 0 The Visible Universe MW galaxy = 20 m = class room Our Galaxy

  20. The Visible Universe is VERY BIG It contains 100,000,000,000 galaxies! A hundred thousand million

  21. The Microwave Background

  22. Universe at Big Bang Universe today 14 B yrs 14 B light-yrs What we witness

  23. 400,000 years Big Bang Very Hot CMB 3000 K cooling ionized foggy atomic transparent hot glowing fog we see a glowing wall of bright fog We cannot see the Big Bang itself It is hidden behind 400,000 light years of dense fog redshift z=1000 orange light microwaves

  24. Human lifespan Conc- eption child teenage Old age 12hr Marathon race Finish 26 miles Start 4 feet CMB is Young and Far 380,000 yr 5 Time (Gyr) 10 0 14 Big Bang here now “nearby” galaxies CMB NGST HST

  25. Observing the Microwave Background Bell Labs (1963) (highlights, there are many others) COBE satellite (1992) WMAP satellite (2003)

  26. The Celestial Sphere Optical Sky Microwave Sky Microwave Sky Stretched

  27. Sound in the Early Universe

  28. Sound waves in the sky Water waves : high/low level of water surface Many waves of different sizes, directions & phases all “superposed” Sound waves : red/blue = high/low gas & light pressure

  29. Sounds are waves of pressure. (in this case: moving through a gas)

  30. gas falls into valleys to make first compression compression dim dim rarefaction bright rarefaction b) it then rebounds out to make first rarefaction bright bright rarefaction compression compression dim The first sound waves c) then back in again to make second compression  the oscillation continues  sound wave created

  31. What does the CMB “sound” like? Three important aspects to perceived sound: A. Volume B. Pitch C. Spectrum Consider each in turn:

  32. dP Pressure dP Po  volume Po Time or position (A) Volume : quiet – loud How much does the pressure vary ? Cosmic sound : dP/Po = 10-4  110 decibels !

  33. (B) Pitch : deep – high What frequencies can we hear ? 20 – 20,000 waves per second (Hertz) v. deep v. high What’s the Cosmic pitch ?? 1 wave every 20,000 – 200,000 yrs !! Too deep to hear, by about 50 octaves!

  34. DEEP? Why is primordial sound so BIG Because the Universe is so: Cathedral Organ Universe Pan Pipes 400,000 light years

  35. (C) Sound Spectrum Sounds usually contain many frequencies A graph of this is called the Sound Spectrum Modern Flute

  36. Sky Maps  Sound Spectra Cannot follow waves in time. Instead use the wave’s spatial appearance Evaluate spatial power spectrum, of waves on the sphere. “frequency” is spherical angular harmonic: ℓ peak trough Lineweaver 1997

  37. The Observed Sound Spectrum fundamental current best data × harmonics ( model) angular wavelength (degrees) Sound “Loudness” sky frequency (~180/°) sound frequency (Hz)

  38. Sound Waves in the Sky The CMB Power Spectrum Relative loudness at different pitch NASA’s WMAP satellite Loudspeaker Loudness Raw CMB sound Frequency Wavelength Lower Pitch Higher Pitch The Microwave Sky Water waves on the ocean surface illustrate sound waves on the CMB “surface” short plus medium plus long all mixed together Microwave brightness, greatly contrast stretched. Brightness differences are also pressure differences Patches smaller than 2º are sound waves

  39. Sound as Diagnostic • Quality of sound reveals the nature of an object • True also for the Universe: • The sound spectrum reveals many properties • Use computer simulations to match data • Two examples: baryon fraction; total density

  40. Geometry of the Universe Open :Ω= 0.8 Flat : Ω= 1.0 Closed: Ω=1.2 Low pitch High pitch Long wavelength Short wavelength

  41. Atomic content of the Universe 2% atoms 4% atoms 8% atoms Low pitch High pitch Long wavelength Short wavelength

  42. The Concordance Model • Age of Universe13.7 Gyr (2%) • Flatness 1.02 (2%) • Atoms 4.4% (9%) • Dark matter 23% (15%) • Dark energy 73% (5%) • Hubble constant (km/s/Mpc) 71 (6%) • Photon/proton ratio 1.6x109 (5%) • Time of first stars 180 Myr (50%) • Time of CMB 380,000yr (2%)

  43. Removing Distortion: C(ℓ)  P(k) The Universe is a poor concert hall ! Distortions are present in the sound spectrum. One can “remove” distortions by using robust computer simulations (eg CMBFAST)