UND scientist seeks to detect 'dark energy'

GRAND FORKS, N.D. — Imagine if you threw a rock in the air and, instead of watching it slow, then drop to the ground, it sped up and disappeared in the sky.

That's what it's like for scientists when they look at the stars and find that the universe, which has been expanding since its beginning, is expanding faster rather than slowing down, according to UND astrophysicist Wayne Barkhouse.

"It's so profound," he said one recent Tuesday in his office. "It's the biggest puzzle in astrophysics in 100 years."

The laws of physics as they are now understood suggest the expansion of the universe should slow under the effects of gravity, he said. The apparent violation of these laws is what makes the accelerating expansion so perplexing, he said.

Barkhouse is part of an international team of scientists trying to better understand this phenomenon using a survey of the night sky to detect an elusive form of energy called "dark energy."

A computer programmer, he has spent the past seven years creating software in preparation for the Dark Energy Survey, which began last month.

COSMIC MYSTERY

Scientists don't know much about dark energy, which appears to have anti-gravity-like properties and is estimated to make up three-quarters of the universe. It's called dark energy because it has not been directly observed, only inferred from observations of other things in the sky.

Two teams of astronomers first discovered dark energy in 1998 while studying supernovae, and several experiments have since confirmed its existence.

"What happens to our universe and the future is interesting because it depends on the explanation for dark energy, what the actual cause is," Barkhouse said.

At first, using known laws of physics, scientists theorized that dark energy can get stronger with time, he said. But that implies it would push things apart so rapidly that galaxies, planets and "all of the atoms in your body would move away from each other," he said.

Since then, scientists have concluded that the value of dark energy must be more than zero, but not very large, he said.

The aim of the Dark Energy Survey is to measure dark energy by measuring the expansion of the universe.

"By knowing how the universe is expanding and knowing what the structure is in terms of galaxies and stars, you get an estimate of the expansion rate of the universe, i.e. dark energy," Barkhouse said.

MASSIVE SURVEY

The project uses the world's most powerful digital camera, mounted on a telescope with a 13-foot-wide mirror, high in the mountains of northern Chile, according to the camera's maker, Fermi National Accelerator Laboratory.

With each snapshot, the 570-megapixel camera would capture images of more than 100,000 galaxies as far away as 8 billion light years.

Over five years, the camera will survey one-eighth of the sky, photographing an estimated 300 million galaxies, 100,000 galaxy clusters and 4,000 supernovae, Fermilab said. The images will go to supercomputers at the University of Illinois at Urbana-Champaign, where Barkhouse had a post-doctoral position prior to coming to UND.

"By doing these observations, that allows us to get a real handle on the amount of dark energy in the universe," he said. "We can narrow down uncertainties so we can get a precise measurement of dark energy."

STILL UNKNOWN?

By the end of the project, scientists should know the pace of dark energy over a large fraction of the universe's age, Barkhouse said. This will allow scientists to rule out competing ideas about the cause of dark energy that predict it should change with time, he said.

However, they still may not know the exact answer.

"We can be in that same situation, even 100 years from now," Barkhouse said. "But this is an area that people are working on a lot, because it has a profound effect on our universe."

More than 120 scientists from the United States, Europe and Brazil have stake in the $15 million Dark Energy Survey.

The U.S. government has also made the project a top priority in space research. It has plans for a space telescope that would measure dark energy and a new ground-based telescope much larger than the one in Chile.

Solving the mystery of dark energy may take five years or it could take 500 years, Barkhouse said, but "the only thing you know is if you don't do anything, nobody's gonna solve it."