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Studying Dark Energy ... at the South Pole

It’s the most plentiful stuff in the universe—and maybe the most mysterious.

But thanks to work being done in Antarctica by a team led by astrophysicist John Carlstrom ’81, scientists may finally be getting a handle on “dark energy.”

Using a 10-meter telescope that captures high-resolution images of what Carlstrom calls “the light left over from the Big Bang,” the South Pole Telescope team is mapping the universe as it existed 14 billion years ago when it was only 400,000 years old—a time before stars or planets had formed. Tracking this leftover light, called cosmic microwave background (CMB) radiation, may hold the key to understanding dark energy.

“It’s like we’re taking snapshots of the universe’s baby pictures,” says Carlstrom, a professor of astronomy and astrophysics at the University of Chicago.

Learning about dark energy is important, Carlstrom says, because it will help explain why and how the universe is rapidly expanding. Scientists had long believed gravity, as explained in Einstein’s Theory of Relativity, would eventually slow down the universe’s expansion, but they’ve now determined its expansion is accelerating. 

But Einstein also conceived of a force that acted like negative gravity by adding what he called the “cosmological constant” to his equations, Carlstrom says.

“Maybe dark energy is this cosmological constant,” he says. But he added scientists still have a lot of work to do figuring out exactly what dark energy is and how it works.

“It’s a huge frontier, and we built this big telescope as one way to go after it,” Carlstrom says. “We can now measure (CMB radiation) on an unprecedented scale; we’re looking at it with a much bigger eye.”

One thing scientists are seeing through this eye is a universe whose galaxies are flying apart. The team at the South Pole is detecting “shadows” of this radiation passing through far-away clusters of galaxies never seen before.

“We’ve learned that parts of the universe that were connected have now become separated by huge distances,” Carlstrom says.

Since all galaxies are moving away from each other and the rate of their movement is accelerating uniformly, scientists are beginning to believe a uniform force—dark energy—must be the engine driving this expansion, he says.

The search for answers about dark energy comes four decades after astronomers, including Vassar grad Vera Rubin ’48, confirmed the existence of “dark matter,” an invisible halo that surrounds galaxies but does not emit or reflect light.

Carlstrom says astronomers now have shown that dark matter comprises about 25 percent of all the stuff in the universe today while dark energy comprises about 70 percent.

“This means that all the stuff our textbooks call matter makes up less than 5 percent of the universe,” Carlstrom says.

He says he plans to resume his work at the South Pole when Antarctica’s “spring” arrives in November and temperatures rise sufficiently to allow planes to land safely.

A 10,000-foot plateau on Antarctica was chosen as the location for the telescope because the skies there are the clearest and driest of any place on earth, Carlstrom says.

The South Pole Telescope collaboration, funded primarily by the National Science Foundation, is led by the University of Chicago. Other members of the team are from Argonne National Laboratory, Cardiff University, Case Western Reserve University, Harvard University, Ludwig-Maximilians-Universität, Smithsonian Astrophysical Observatory, McGill University, the University of California at Berkeley, University of California at Davis, University of Colorado at Boulder, and the University of Michigan, as well as individual scientists at several other institutions.

–Larry Hertz