Mapping the Dark Cosmos

Dark matter—the unseen stuff that makes up more than four-fifths of the matter in the universe—is finally coming into view. What we see may change our entire picture of reality.

More than 80 percent of the matter in the universe consists of an unknown substance that cannot be seen through any telescope nor detected in any lab. This invisible stuff interacts with normal matter only through gravity, which is how astronomers first inferred its existence. More recently, computer models have demonstrated that dark matter is actually crucial to the visible realm. Without it, galaxies never would have pulled together. There would be no stars. There would be no people. 

Although astronomers still do not know exactly what dark matter is, in 2012 they learned a lot more about how it works. One team traced the way it spreads its tentacles throughout the cosmos. And another found hints that dark matter may not always be invisible after all.

Last January, Ludovic van Waerbeke of the University of British Columbia and Catherine Heymans of the University of Edinburgh announced that they had mapped a web of dark matter more than 1 billion light-years across. "That's the largest map ever made of dark matter," Van Waerbeke says. Although the dark stuff cannot be observed directly, its gravity bends light from any galaxies shining through it. Measuring the amount of bending reveals how much dark matter is present. 

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