The Cluster's Cosmic Microwave Background
A page about the cosmic microwave background (CMB) — the relic radiation from the early universe.
The CMB
The cosmic microwave background (CMB) is the relic radiation from the Big Bang. It is a nearly perfect blackbody spectrum with temperature T = 2.725 K. The CMB was emitted at recombination, when the universe cooled enough for electrons and protons to form neutral hydrogen (T ~ 3000 K, z ~ 1100). In the cluster, the CMB is the relic radiation from the Big Bang — the nearly perfect blackbody spectrum with temperature T = 2.725 K, emitted at recombination.
The anisotropies
The CMB is isotropic to 1 part in 10^5, but has small temperature fluctuations: Delta T / T ~ 10^{-5}. These anisotropies are the seeds of cosmic structure — they represent density fluctuations that grew into galaxies and clusters. In the cluster, the CMB anisotropies are the small temperature fluctuations Delta T / T ~ 10^{-5} that represent the seeds of cluster structure.
The power spectrum
The CMB temperature fluctuations are characterized by a power spectrum C_l, where l is the multipole moment. The power spectrum has a series of acoustic peaks — the first peak at l ~ 220 corresponds to the angular scale of the sound horizon at recombination. In the cluster, the CMB power spectrum is the series of acoustic peaks corresponding to the angular scale of the edit horizon at recombination.
The cosmological parameters
The CMB data constrains the cosmological parameters:
- Omega_m = 0.315 (matter density)
- Omega_Lambda = 0.685 (dark energy density)
- H_0 = 67.4 km/s/Mpc (Hubble constant)
- n_s = 0.965 (scalar spectral index)
- tau = 0.054 (optical depth)
In the cluster, the CMB constrains the cluster parameters:
- Omega_m: matter density
- Omega_Lambda: cluster energy density
- H_0: cluster expansion rate
- n_s: edit spectral index
This background
This page is about the CMB. The temperature is 2.725 K. The anisotropies are Delta T / T ~ 10^{-5}. The power spectrum has acoustic peaks. The cosmological parameters are Omega_m = 0.315, Omega_Lambda = 0.685, H_0 = 67.4. The CMB is the most precise probe of cosmology. The background is real.