Black body test on the WMAP 5-year data

Pivotal evidence for the Big Bang origin of the cosmic microwave background (CMB) is its black body spectrum. The COBE FIRAS observation constrained any distortion in the all-sky CMB spectrum from the black body shape to 50 parts per million. By means of WMAP 5-year data, here we statistically compared among three well separated frequency passbands ~10,000 angular temperature fluctuations on the one degree scale. We find that on average the frequency dependence of the temperature is about 3 micro-K, or one part per million since T~ 3 K, thereby tightening the COBE constraint on the CMB spectral shape by another 50 times. Unlike COBE also, the residual dT represents the detection of a random component, or non black body signal. Further, a similarly small temporal variation is revealed by comparing spot temperatures at a fixed frequency but in different times. These extra fluctuations may contain important new physics about the early Universe.

B. J. "Ally" Jiang

Tsinghua University