"Enormous cosmic voids and giant concentrations of matter have been observed in a new galaxy survey, one of the biggest completed so far. One of the voids is so large that it is difficult to explain where it came from.
Called the Six Degree Field Galaxy Survey (6dFGS), the project scanned 41% of the sky, measuring positions and distances for 110,000 galaxies within 2 billion light years of Earth.
No previous survey has covered as much of the sky at such a distance. The Sloan Digital Sky Survey (SDSS), which is based in the northern hemisphere, has probed about twice as far but covers only 23% of the sky....
...Scientists are still analysing the new map, but a few features stand out immediately. The biggest concentration of matter seen by the survey is a previously known giant pileup of galaxies called the Shapley supercluster, which lies about 600 million light years from Earth.
The survey also found some enormous voids – regions of space that are relatively empty, including one that is about 3.5 billion light years across....
...In fact the newly found void is so large that it is difficult to fit into our present understanding of the universe on the largest scales. Computer simulations show that gravity causes galaxies and galaxy clusters to get closer together over time, with voids growing between the clusters.
But the finite time available since the big bang makes it difficult to explain a void as large as the one found in this survey (other researchers, however, say galaxy maps already hint at the existence of such large-scale structures)...."