1Black-Body Radiationfor large λ: (Rayleigh-Jeans tail)Black bodyalso… dilute black body [CO Sect. 3.4]Isotropy of the Cosmic Microwave BackgroundDipole Anisotropy~ 1 part in 300...Blue = 0oKRed = 4oKBlue = 2.724oKRed = 2.732oKDipole AnistropyÎmotion of Sunthrough Universe.After removing dipoleRed – blue = 0.0002oK• Dipole Anistropy ~ 1 part in 300• 600 km/sec motion of Local Group in grav. field of larger scale mass concentrations. LocalGroupfor v << c(29.62)for large λBlack body2Isotropy of the Cosmic Microwave BackgroundIs the universe really isotropic?• No quadropole anisotropy in CMB Î Rx/Ry= 1±ε, ε < 10-9• Vorticity:(ω/Ho) < 10-8for 0.05 < Ω < 1Dipole Anisotropy~ 1 part in 300...Blue = 0oKRed = 4oKBlue = 2.724oKRed = 2.732oKDipole AnistropyÎmotion of Sunthrough Universe.After removing dipoleRed – blue = 0.0002oKWhen did decoupling occur?• Saha equation: Collisional ionization rate = Recombination rate• Solve for = 1, usingÎ R ~ 7.2x10-4 T ~ 3800 K• Taking composition and radiative transfer into account:Tdec= 2970K zdec= 1089Rdec= 9x10-4tdec= 118,000 yrs.Decoupling also called “recombination”(8.8)3The Radiation EraDuring the Radiation Era:RdR ∝ dtR ∝ t1/2instead of R ∝ t1/2in matter
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