cold spot

The cold spot (or CMB cold spot or WMAP cold spot) is a region of the celestial sphere (a few tens of square degrees) in which the cosmic microwave background (CMB) indicates a slightly lower temperature than the rest, a difference on the order of 70 millionths of a kelvin. The temperatures indicated by the CMB's black-body spectrum across all the different portions of the celestial sphere generally form a tight Gaussian distribution (a type of random distribution) around a specific value, about 2.72548 K. However, at least one test of gaussianity indicates this region's temperature is anomalously low, suggesting it is an unlikely characteristic if there is a physical reason for the randomness seen across the whole sky. There has been some investigation regarding whether the apparent colder region corresponds to a void or voids in that direction, showing the low temperature due to a Sachs-Wolfe effect.