From Yahoo News:
The team at the University of Minnesota said the void is nearly a billion light-years across and they have no idea why it is there."Not only has no one ever found a void this big, but we never even expected to find one this size," said astronomy professor Lawrence Rudnick.
Writing in the Astrophysical Journal, Rudnick and colleagues Shea Brown and Liliya Williams said they were examining a cold spot using the Wilkinson Microwave Anisotropy Probe satellite, and found the giant hole.