Road trip: Fermi National Accelerator Laboratory, part 2

Posted by Rich Talcott
on Monday, December 6, 2010

When you hear the name Fermi National Accelerator Laboratory, or Fermilab for short, cosmology likely isn’t the first thing to cross your mind. But Fermilab researchers are busy building an astronomical camera that could help confirm that dark energy rules the current universe — or the unsettling alternative that scientists don’t understand gravity very well.

Astronomy Associate Editor Liz Kruesi suits up to visit the clean room where scientists test the CCD chips for the Dark Energy Camera. Rich Talcott photo
The Dark Energy Camera was the reason Associate Editor Liz Kruesi and I made the trek to Fermilab in Batavia, Illinois, November 17. The laboratory opened its doors to us and about 20 others to show the camera and to explain the vital role it will play in the upcoming Dark Energy Survey (DES).

In 1998, cosmologists first learned that gravity’s influence has been dwindling ever since the Big Bang. Early in cosmic history, gravity’s attractive force slowed down the universe’s expansion. But roughly 5 billion years ago, the expansion rate started to speed up. The current best guess: A mysterious anti-gravity force, dubbed “dark energy,” has taken over. Scientists think dark energy now constitutes nearly three-quarters of the mass and energy in the universe.

But being scientists, they want to know for sure. Enter the DES. This survey will measure some 300 million galaxies out to a distance of about 9 billion light-years. It will study dark energy using four methods: the abundance of massive galaxy clusters, the gravitational lensing of light by galaxies and clusters, the large-scale clustering of galaxies, and the brightnesses of distant supernovae.

The Dark Energy Camera rests inside its holding cage at Fermilab. Sometime early next year, the camera will make its way to Chile, where it will sit at the prime focus of the 4-meter Blanco Telescope. Rich Talcott photo
The first two techniques will yield answers that depend on the geometry of the universe while the final two techniques depend on gravity. If all four give the same results, then dark energy behaves the way scientists theorize it should. If the methods yield different answers, however, then dark energy doesn’t exist and the leading theory of gravity — Einstein’s general theory of relativity — has problems.

To accomplish the survey, Fermilab scientists will attach the Dark Energy Camera to the 4-meter Blanco Telescope at Cerro Tololo, Chile. The 4-meter scope offers a perfect combination of a wide field of view and the ability to go deep. The 570-megapixel camera contains 74 CCD chips, and a single image captures an area of sky 20 times the size of a Full Moon. The camera will operate 105 nights per year starting in September 2011, and continue for 5 years.

The 4-meter Blanco Telescope sits in its dome at the summit of Cerro Tololo in Chile. The 40-year-old telescope will get a new lease on life when the Dark Energy Camera starts operating next September. Rich Talcott photo
The camera will send a few hundred images per night to the University of Illinois, Urbana-Champaign, where supercomputers will crunch the digital data. And, with any luck, in 5 years scientists will have a better grasp on the nature of dark energy, and of gravity itself.

Related blog:
Road trip: Fermi National Accelerator Laboratory, by Liz Kruesi, associate editor

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