July 6, 2014 - IT HAS been called a bruise on the sky â€“ a curious cold spot in the afterglow of the big bang that has sparked wild cosmic theories attributing it to a run-in with another universe or a wrinkle in space-time.
Now it seems the answer may be a little more mundane: the biggest known hole in the universe.
The cold spot appears in maps of the cosmic microwave background (CMB), the earliest light emitted in the universe. Temperature variations in the light show up as a mottled pattern in the maps, which can be explained if quantum fluctuations at the universe's birth were stretched out by a brief but spectacular cosmic growth spurt known as inflation.
But some features in the maps don't fit into the leading models of inflation. For example, the relatively even pattern of the CMB is marred by an unusually large cold region. Scientists have struggled to explain it, suggesting a number of ideas that require exotic physics or even evidence for a multiverse.
A much simpler explanation is that the cold spot is caused by a giant void
in the universe. The cosmos consists of a web of bright galaxies and clusters surrounded by dark pockets that contain little matter. Radiation loses energy when it crosses these empty regions, so a large void could cause a cold spot in our CMB maps.