AMUNDSEN-SCOTT STATION, Antarctica -- Anywhere else it would be a big telescope, as high as a 7-story building, with a main mirror measuring 32 feet wide. But at the South Pole, it seems especially large, looming over a barren plain of ice that gets colder than anywhere else on the planet.
Scientists built the instrument at the end of the world to search for clues that might identify the most powerful, plentiful but elusive substance in the universe -- dark energy.
First described nine years ago, dark energy is a mysterious force so powerful that it will decide the fate of the universe. Having already overruled the laws of gravity, it is pushing galaxies away from one another, causing the universe to expand at a faster rate.
Though dark energy is believed to account for 70% of the mass of the universe, it is invisible and virtually undetectable. Nobody knows what it is, where it is or how it behaves.
"If you see it in your basement, you better get back on your medication," University of Chicago cosmologist Rocky Kolb said jokingly. But he knows better than most about the high priority the world's governments and scientists have placed on getting a better understanding of the invisible force.
"Many think dark energy is the most important problem in physics today," said Kolb, who served as chairman of the Dark Energy Task Force, convened in 2005 by the U.S. Department of Energy, NASA and the National Science Foundation.
First mission
Swinging its massive mirror skyward, for the last few months the South Pole telescope has begun to search the southern polar heavens for shreds of evidence of dark energy. Controlled remotely from the University of Chicago, the $19.2-million telescope has succeeded in its first mission: finding unknown galaxy clusters, which are clues to the emergence of dark energy.
John Carlstrom, a veteran South Pole astronomer and University of Chicago astrophysicist, is heading the international team that designed and constructed the telescope. The problems his team are trying to solve are 21st Century, as is much of the technology they use, but their methodology is old school.
For thousands of years, astronomers have been puzzling out the size, shape and chemistry of the universe, first by naked eye and then -- for the last 400 years -- with increasingly powerful and sophisticated telescopes. Mostly they study the motion of large objects and apply the known laws of physics to analyze them.
The telescope can't go looking for dark energy directly. Instead, it gathers information for researchers to gain a better understanding of the mysterious force, by tracing how it emerged and changed over billions of years.
To do that, scientists will use the South Pole telescope to search for enormous clusters of galaxies -- the last structures in the universe to be forged by the force of gravity after the Big Bang.
First, gravity formed the stars, then the galaxies, and finally vast clusters containing 50 to 1,000 galaxies.
But at some point, dark energy got the upper hand over gravity, gradually stopping formations and pushing galaxies away from one another.
"It's not incorrect to think of dark energy as acting like negative gravity," Carlstrom said.
In other words, it is a force that causes all physical matter to push away rather than collapse together.
The idea behind the South Pole telescope is to trace how many galaxy clusters formed at different periods in the history of the universe, and then determine when dark energy slowed or stopped their formation.
"We're looking at a tug-of-war with dark energy and gravity trying to expand or collapse the universe," said Carlstrom, 50.
Ideal location
Galaxy clusters are rare, holding perhaps just 1% of all the stars in the universe. Most are so far away and faint that most optical and radio telescopes cannot detect them.
Instead, scientists look for tiny variations in temperature of the remnants of the first light in the universe, emerging about 400,000 years after the Big Bang. Slightly warmer spots in the background indicate the presence of the dim, hard-to-locate galaxy clusters.
And the South Pole -- albeit inhospitable -- is the best place on Earth to do that.
Humidity in the atmosphere would distort signals the telescope receives and the picture it makes. But there is little water vapor at the South Pole. Even though the pole sits on a massive, million-year buildup of ice 10,000 feet deep, the area is a natural desert -- the air is dry, and it rarely snows.
In addition, because of the tilt of the Earth's axis, the pole for nearly half the year is bathed in 24-hour-a-day darkness.
That allows researchers to focus the telescope on one part of the sky for long periods of time.
Eventually, when astronomers know more about how to look at dark energy itself, the quest may require powerful space-based telescopes, said Rocky Kolb of the Dark Energy Task Force.
"We in astronomy think dark energy is a billion-dollar question," he said. "We feel it is that fundamental. It is a big question that will require a big effort to answer it."
January 6, 2008
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