A mysterious cold spot in the cosmic microwave background could be a cosmic defect called a “texture” that was left over from the aftermath of the Big Bang, according to physicists in Spain and the UK. If confirmed, the existence and properties of such a spot would provide physicists with a unique window on the early universe and allow them to test different theories for the unification of the fundamental forces of nature (Science DOI: 10.1126/science.1148694).
The cosmic microwave background (CMB) was born when the universe was about 380,000 years old. Before this time, space was filled with hot plasma that did not allow light to travel very far without being scattered. But as the universe expanded, the plasma cooled enough to allow neutral atoms to form. This “decoupling” of matter and radiation suddenly enabled photons to travel across space largely unimpeded, their wavelengths being stretched over time to produce a faint glow of radiation in the microwave region that we can detect today.
While the CMB is remarkably uniform, it appears to contain a cold spot that is over a billion light years across. The spot was first seen in images taken by NASA’s WMAP satellite in 2004, as it mapped out the tiny fluctuations in the CMB’s temperature. Various possibilities have been suggested, such as instrumental effects, foreground contamination from the Milky Way, the effect of rotating universes and giant voids bereft of galaxies – but none of these are very convincing.