To the multitude of places in the universe where no human has gone before add an area where no matter seems to have gone, either. Astronomers have discovered an enormous zone that appears to contain nothing except the faint radiation left over from the big bang. So far, no one knows what could have caused the zone, and the discovery could force astronomers to revise some of the fundamental assumptions about the structure of the universe.
Outer space might seem empty, but even between the galaxies it can teem with gas and dust, as well as elusive dark matter. Radiation also abounds, including the cosmic microwave background (CMB) from the big bang. In some parts of the cosmos, there is nothing but this background radiation. A leading model, known as inflation, suggests that shortly after the big bang, the universe underwent an exponential growth spurt that established its structure. The inflation model predicts that these voids should be roughly comparable in size and number to the galaxy clusters.
But now, researchers have discovered a zone of emptiness that dwarfs all other objects in the universe. A team from the University of Minnesota, Twin Cities, had been studying data from the Very Large Array Sky Survey, which is mapping the entire universe with radio waves. The team members focused on one part of the survey where the temperature of the CMB is lower than normal. This cooling is significant because interactions with both visible and dark matter warm the CMB slightly, and so the team suspected that matter was absent.
Further observations of the zone, located between 6 billion and 10 billion light-years away, revealed it to be not only devoid of galaxies but also about a billion light-years wide, the team will report in an upcoming issue of The Astrophysical Journal. "What we're suggesting is that there is no matter in this void, either normal or dark," says radio astronomer and co-author Lawrence Rudnick.
Concluding that the zone is free of dark matter might be premature, cautions astrophysicist Harvey Tananbaum of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. Making that determination is difficult and will require confirmation, he says. Meanwhile, cosmologist Paul Davies of Arizona State University in Tempe says the discovery is "potentially very important" for testing theories about the very early universe. The potential deviation from the inflation model is "a tantalizing pointer to some new physics at the dawn of existence."
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