For most people, the term “3-D” probably brings to mind cheap, clunky glasses and hefty movie-ticket prices, but seeing the world—or universe—in three dimensions has uses well beyond popcorn entertainment. One of astronomy’s greatest challenges is determining how far away various points are from Earth. By envisioning the universe in 3-D, astronomers can track how it has changed since it began with the Big Bang 13.7 billion years ago, and perhaps solve some of the universe’s greatest mysteries.
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Investigators with the Sloan Digital Sky Survey have created the biggest 3-D map of the distant universe ever made, and they’ve done so using a novel approach. Instead of pointing a telescope at the sky and focusing on, say, a specific galaxy, the survey has taken broader snapshots. It has collected light from 14,000 quasars located some 9 billion to 11 billion light-years away. These bright objects—the brightest in the universe—are powered by supermassive black holes at centers of active galaxies. Their light filters through clumps of hydrogen gas between us and the quasars, essentially creating shadows that enable scientists to determine the size, shape and distance of those clumps.
Trying to create such a map using existing means, like the Hubble Space Telescope, would be akin to photographing the sky through a straw and “would take something like 100,000 years,” says Sloan investigator David Schlegel of the Lawrence Berkeley National Laboratory. Doing so with the Sloan survey’s telescope, which can capture an area 40 times larger than the moon in a single shot, has taken only a few years. “That’s what’s exciting about this,” Schlegel says. “We’ve actually shown that there’s another way to do this.”
The hope is that the map will help scientists get at [the mystery of dark energy and dark matter], the primary constituents of the universe. Discovered only in the past few decades, dark energy and dark matter together compose 96 percent of the universe. The former influences the rate of the universe’s expansion, but astronomers are in the dark about them (as it were). “We know very little,” Schlegel says. “But we do know that that stuff does effect the history of the universe, and it affects how fast the universe has been expanding in time, and that’s actually what we’re using the map to study.”
What’s the next step for the Sloan survey? Not to turn the 3-D map into a motion picture, that’s for sure. “The folks at Pixar could probably do a great job at this,” Schlegel says, “but we can’t.” Instead, he hopes to be able to map the “middle ground” of the universe—between 5 million and 10 million light-years away, “the time dark energy becomes important”—which astronomers have had difficulty studying so far. “We’re looking at other ideas that can let us do that with telescopes on the ground,” he says. “I think we can do it.”