AS7009, 2009 Outline  Introduction to the CMBR Lecture 7  History of CMBR research  Support for the model  Properties of the CMBR  Temperature  The dipole anisotropy  Small -scale temperature fluctuations  Origin of the CMBR  Recombination  Decoupling  Last scattering surface  Small -scale temperature fluctuations  Cosmological information Covers chapter 9 in Ryden

”for their discovery of the blackbody 2006 Nobel prize in Physics form and anisotropy of the cosmic microwave background radiation ”

John C. Mather George F. Smoot NASA Goddard Space University of California Flight Center Berkeley, CA, USA Greenbelt, MD, USA

Cosmic Microwave Background Radiation (CMBR) - Quick Facts - History of CMBR research I

 Comes from all directions in the sky  Black body spectrum with: ≈  T0 2.73 K  Peak wavelength ≈ 2 mm Nobel prize to  Close to isotropic , except for: Smoot and Mather  Large -scale doppler (dipole ) anisotropy for their work with COBE due to our motion with respect to the CMBR  Small -scale temperature fluctuations due to density fluctuations at z ≈ 1100

1 History of CMBR research II History of CMBR research III

 1934: First prediction of the existence of the  1992: COBE satellite ≈ CMBR  Close to perfect BB, with T ≈2.73 K  Large -scale dipole  Tolman : Expanding should be filled by  Small -scale temperature fluctuations (~10 -5 K) thermal radiation its hot past  Late 90s: MAXIMA & BOOMERanG balloons  1948: First prediction of the current CMBR 1948: First prediction of the current CMBR  Small -scale temperature and polarization variations temperature  2003 - now : WMAP satellite ≈  Gamow , Alpher & Herman: T 0 5 K  Full -sky maps of polarization and small -scale temperature  1965: CMBR discovered by Wilson & Penzias variations ≈  2009 ( launched May 14): satellite  Temperature measured to be T 0 3.5 K  Superior polarization measurement  Planck -scale physics ???

Hot Why is there a CMB? Cold, dark

 Early Universe (t<240 000 yr): Hot → Galaxies  Baryons ionized form  Universe opaque to photons e  Photon -baryon plasma stanc Now or di Time  Cosmic expansion → Here/now  Universe neutral at t~240 000 yr  Universe transparent to photons

Photon trajectories from the Early Support for the Big Bang model Universe

 Expansion of the Universe  The primordial abundances of light Now elements  The age consensus Neutral d Ionize  The CMBR fog) (cosmic The temperature of the plasma was about 3000 K when the CMBR was emitted. Cosmic expansion → Energy loss due to → T ≈ 2.73 K

2 The CMBR as support for the Big Bang model I The CMBR as support for the Big Bang model II

 Existence of the CMBR :  Temperature of the CMBR:  Richard Tolman (1934): Expanding Universe  T0 = 2.73 K fits Big Bang model should be filled with thermal radiation from hot (but note: the a priori prediction was not this precise)

past  Big bang model predicts: T (z) = (1+z) T 0  CMBR ≈ ”Afterglow of the Big Bang” Confirmed by measurements up to z ≈ 3  Difficult to understand in Steady State-type  Small-scale temperature anisotropies:  Results in cosmological parameter values consistent with other methods

Properties of the CMBR I: Properties of the CMBR II: Spectral shape and temperature The Dipole Anisotropy

Doppler shift due to our movement (dominated by the motion of the Sun around the Milky Way and of the Local Group Temperature average over all directions: ≈ 2.73K towards Hydra) relative to the CMBR

Suggestion for literature exercise: Properties of the CMBR III: Strange CMBR anisotropies Small -scale temperature fluctuations

Overall CMBR, including Doppler dipole

CMBR with dipole subtracted

CMBR with Milky Way and nearby structure subtracted → Small-scale temperature fluctuations (RMS 10 -5 K) The ”Axis of evil ” & the cold spot : Very important for cosmological model fitting! Signatures of non -standard cosmology ?

3 Origin of the CMBR: Origin of the CMBR: Radiation -matter equality Important Concepts Matter  Radiation -matter equality Radiation Density  Photon decoupling Matter- domination  Recombination Radiation- domination  Last scattering surface  The Sachs -Wolfe effect Time  Acoustic peaks Radiation-matter equality happened at z ≈ 3570, T ≈ 9730 K, t ≈ 47 000 yrs

Origin of the CMBR: Origin of the CMBR: Decoupling I Decoupling II During radiation-domination, and during a short period Rate of scattering interactions for this process: in the matter-dominated era, photons kept the atoms ionized c Γ = = n σ c : λ e e γ + e- → γ + e- This process freezes out when: Mean free path of photons: Γ < H λ = 1 n σ This leads to decoupling of photons from the baryonic plasma e e → Baryons and photons evolve separately

Origin of the CMBR: Origin of the CMBR: Recombination Last Scattering Surface At around the same time, the expansion of the Universe Last scattering surface causes the energy of the photons to drop below 13.6 eV → Hydrogen starts (re)combining and the Universe goes from ionized to neutral, which speeds up the decoupling Now Recombination happened at z ≈ 1370, T ≈ 3740 K, t ≈ 240 000 yrs Neutral nized Photon decoupling happened at Io mic fog) z ≈ 1100, T ≈ 3000 K, t ≈ 350 000 yrs (cos CMBR photons reach us from a fog-like ’wall’. This last scattering surface is located at z ≈ 1100, T ≈ 3000 K, t ≈ 350 000 yrs

4 Origin of the CMBR: The Sachs -Wolfe effect Small -scale temperature fluctuations Density fluctuations present at the time of last scattering are evident as spatial temperature fluctuations in the CMBR Φ l Recall : θ = Underdense Gravitational redshift dA Gravitational blueshift region

In the benchmark model , the horizon distance at zCMBR Average corresponds to θ ≈1° H density θ θ Potential energy  On scales > H: Primordial CDM density fluctuations θ θ  On scales < H: Acoustic oscillations in the photon - baryon fluid Overdense region

The late/ integrated Sachs -Wolfe effect (or Rees -Sciama effect ) The Angular Power Spectrum I The gravitational red/blueshift of CMBR photons due to structure along the line of sight towards the last scattering surface. When studying CMBR temperature fluctuations Static potential well → Blueshift climbing in, redshift climbin out (no net effect) as a function of angular scale, one usually plots: But net /blueshifts will happen if the potential well gets shallower/deeper while crossing!  (ll + )1  2/1 ∆ =  C  T T  2π l  Is a huge, expanding void where : along the line of sight the reason for the CMBR l is the multipole (note : high l means small θ ) ’cold spot’? δT C is the angular correlatio n function of l T

The Angular Power Spectrum II Cosmological Information I WMAP 5-year data and model fit Ω = − Ω + Ω ⇒ k 1 ( M Λ ) K) µ ( Ω = 0 ⇒ Flat

T k ∆

The positions of the CMBR peaks are very sensitive to the geometry. The observed positions 3rd 2nd 1st peak indicate that our Universe is very close to flat! Temperature fluctuations

Primordial Acoustic oscillations

5 Cosmological Information II

Mild degeneracy: The amplitude ratios of the first three peaks are sensitive to the baryon density

Cosmological Information III Cosmological Information IV

Mild degeneracy: The amplitude ratios of Example of strong the first three peaks degeneracy: are also sensitive Hubble constant and Ω to the CDM Λ variations density mimic each other (if other parameters are held fixed)

Cosmological Information V Cosmological information VI

Example of strong Benchmark model degeneracy: Ω Ω Hubble constant and M=0.3, Λ=0.7 Ω variations -1 -1 Λ H0=72 km s Mpc mimic each other (if other parameters are held fixed)

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