Search for Dark Energy Heats Up at the Bottom of the World


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“We’re looking at a tug-of-war with dark energy and gravity trying to expand or collapse the universe.”

John Carlstrom, South Pole astronomer and University of Chicago astrophysicist.

A big telescope, as high as a seven-story building, with a main mirror measuring 32 1/2 feet across was built at the Amundsen-Scott Station in the Antarctica  looming over a barren plain of ice that gets colder than anywhere else on the planet. The South Pole Telescope (SPT), a microwave telescope, has been in use since February 16, 2007.

The instrument at the far end of the world was built so scientists can search for clues that might identify the most powerful, plentiful but elusive substance in the universe — dark energy.

The telescope helps scientists to reveal new details regarding a mysterious phenomenon called dark energy, which makes the expansion of the universe accelerate. Albert Einstein's famous "cosmological constant," which is one possibility for the dark energy, also will come under the telescope's scrutiny. The "gravity" of dark energy is repulsive. It pushes the universe apart and overwhelms ordinary gravity, the attractive force exerted by all matter in the universe. Dark energy is invisible, but astronomers will be able to see its influence on clusters of galaxies that formed within the last few billion years.

"With the South Pole Telescope we can look at when galaxy clusters formed and how they formed. That is critically dependent on the nature of the dark energy, this elusive component of the universe," said Carlstrom, who heads the project. "We've only known about dark energy for a few years. No one really knows what it is."

"One of our main goals is to figure out what the dark energy is," said center Director Bruce Winstein, the University's Samuel K. Allison Distinguished Service Professor in Physics. "Is it a cosmological constant or is it dynamical? The South Pole Telescope holds the promise to give us a lot of new, valuable information on this.". 

First described a decade 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 an ever faster rate.

Though dark energy is believed to account for 70 percent of the universe's mass, it is invisible and virtually undetectable. Nobody knows what it is, where it is or how it behaves.

Solving the mystery of dark energy is would explain the history and future of the universe and generate new understanding of physical laws that, applied to human invention, almost certainly will change the way we live — just as breakthroughs in quantum mechanics brought us the computer chip.

Swinging its massive mirror skyward, the South Pole Telescope (SPT) searches the southern polar heavens for shreds of evidence of the elusive stuff. Controlled remotely from the University of Chicago, the $19.2 million telescope quickly succeeded in its first mission: finding unknown galaxy clusters, clues to the emergence of dark energy.

The cold, dry atmosphere above the South Pole allows the SPT to more easily detect the cosmic microwave background radiation (CMB), the afterglow of the big bang, with minimal interference from water vapor. On the electromagnetic spectrum, the CMB falls somewhere between heat radiation and radio waves.

The CMB is largely uniform, but it contains tiny ripples of varying density and temperature. These ripples reflect the seeds that, through gravitational attraction, grew into the galaxies and galaxy clusters visible to astronomers in the sky today. One of the SPT’s first key science project was to study small variations in the CMB to determine if dark energy began to affect the formation of galaxy clusters by fighting against gravity over the last few billion years.

Galaxy clusters (image at top) are groups of galaxies, the largest celestial bodies that gravity can hold together. Our galaxy, the Milky Way, is in one of these clusters, which actually change with time.

The CMB allows astronomers to take snapshots of the infant universe, when it was only 400,000 years old. No stars or galaxies had yet formed. If dark energy changed the way the universe expanded, it would have left its “fingerprints” in the way that it forced galaxies apart over the deep history of time. Different causes would produce a different pattern in the formation of galaxy clusters as reflected in the distortion of the CMB.

According to one idea, dark energy could be Einstein’s cosmological constant: a steady force of nature operating at all times and in all places. Einstein introduced the cosmological constant into his theory of general relativity to accommodate a stationary universe, the dominant idea of the day. If Einstein’s idea is correct, scientists will find that dark energy was much less influential in the universe five billion years ago than it is today.

“Clusters weren’t around in the early universe. They took a long time to evolve,” Carlstrom said.

Another version of the dark energy theory, called quintessence, suggests a force that varies in time and space. Some scientists even suggest that there is no dark energy at all, and that gravity merely breaks down on vast intergalactic scales.

Scientists expect the telescope to detect tens of thousands, of galaxy clusters within a few years.

Posted by Casey Kazan.

Source:

http://www-news.uchicago.edu/releases/07/070226.southpole.shtml

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