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Fermilab scientists finalized testing of the Dark Energy Camera and look forward to "first light," the first use of the camera in August.


Cosmic camera focuses on dark energy

by Chelsea Whyte and Justin Eure
March 10, 2011


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Chelsea Whyte/MEDILL

The Dark Energy Camera during testing at Fermilab. It is mounted on a structure that simulates the telescope where it will provide an eye to view dark energy.

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Chelsea Whyte/MEDILL
 

Scientists and engineers around the world contributed the pieces that created the Dark Energy Camera. The camera parts will be shipped to Chile for assembly on the Blanco Telescope over the next six months. (Click to enlarge)

A global team builds a camera

The Dark Energy Survey is an international collaboration of 120 scientists and engineers from 23 organizations. It relies on a camera made from pieces fabricated all over the world and shipped to Batavia for test-runs at Fermilab.

  •  The five filters of the camera, which will give the images color and are the largest ever produced, were made by Asahi Spectra, headquartered in Tokyo, Japan.
  •  The shutter is the largest of its kind and was manufactured by Bonn University in Germany.
  •  The University of Michigan provided the filter changer.
  •  The hexapods, which provide the focus and alignment system, were made by ADS International in Italy.
  •  The lenses were cast by Corning Precision Lens in New York and polished by SESO in France, and assembled into the corrector in England. The largest of these lenses will weigh 380 pounds.
  •  The Lawrence Berkeley National Laboratory in California developed the CCDs, the digital image sensors.
  •  Collaborators in Barcelona and Madrid contributed the electronics for the CCD readout boards.
  •  Ohio State University and The University of Illinois at Urbana-Champaign developed the instrument control software.
  •  Fermilab was the site of assembly and testing of the camera.


This camera isn’t your average point-and-shoot.

The Fermi National Accelerator Laboratory near Batavia just completed testing it, one of the world’s largest and most powerful cameras.

The 570 megapixel Dark Energy Camera travels to Chile this month for installation on the 4-meter Victor M. Blanco Telescope to try to determine how dark energy – the mysterious substance making up more than 70 percent of our universe - is accelerating the expansion of our universe.

“It’s a very large digital camera,” said Josh Frieman, an astrophysicist at Fermilab and the director of The Dark Energy Survey, which aims to defining the mysterious force acting on our universe. The enormous camera has 570 megapixels and uses 5 lenses, each 3 feet in diameter.

“Today you can get a handheld camera with maybe 10 or 15 megapixels, so it doesn’t sound like so much, but these are very special pixels because they’re very sensitive and they operate at very low temperatures,” he said. 

The Dark Energy Camera won’t exactly take a picture of dark energy. Afterall, you can’t take a picture of something you can’t see. But just as if you’re studying gravity by observing its effects on, say, an apple falling from a tree, the Dark Energy Camera will photograph dark energy’s impact on supernovae and galaxy clusters.

The camera is cooled to -200 degrees Fahrenheit to limit any blur caused by heat vibrating materials within the instrument. The step insures clearer pictures of very faint galaxies.

“We want to map out a large region of the sky and we want to get fine detail about each point on the sky, so that’s why we have such a big camera. With a single snapshot, we can get a lot of information about each point in that region of the sky,” Frieman said.

The Dark Energy Survey will use this mega-camera to survey 300 million galaxies and 4,000 supernovae over 525 nights spread over a few years. The camera images will help unravel the mysteries behind dark energy and the accelerating expansion of the universe.

“The universe began expanding with a Big Bang some 14 billion years ago,” Frieman said. “But we expected that expansion to be slowing down over time because of gravity attracting objects to each other.”

Instead, in 1998, a significant discovery found that the expansion of the universe is actually speeding up.
Since then, several projects have confirmed the acceleration of the expanding universe by observing how supernovae and galaxy clusters are moving out toward the edges of the universe.

“This is something that to me, by now, is incontrovertible,” Frieman said. “The universe is speeding up. I wouldn’t have said that 10 or 12 years ago, but now I think the evidence is very strong.”

This accelerating expansion has caused scientists to question what we know about our universe and come to the conclusion that either our understanding of the law of gravity isn’t accurate, or there’s something out there pushing mass apart rapidly.

“The last decade has been the decade of confirming the discovery that the universe is speeding up and what we want to try to do in the next decade is try to figure out why it’s speeding up,” Frieman said.

Gravity, as we currently understand it, pulls matter together. Think of Newton and his famous apple falling toward the ground.

“Mass pulls the universe together, but dark energy is doing the opposite, pushing everything apart,” said Richard Massey, astronomy fellow at the Royal Observatory in Edinburgh. “It effectively acts as a kind of anti-gravity.”

If you toss that apple up in the air on Earth, it would fall back down into your hand, pulled by gravity.
“On the other hand,” said Massey, “dark energy appears to be something completely unfamiliar to us in our everyday lives. If you threw an apple into the air, and dark energy had its way, the apple would not come back down, but accelerate upwards, racing off into space.”

Dark energy isn’t common here on the relatively tiny planet Earth. But it is thought to be acting homogeneously on the large scale objects in universe. “We think dark energy is homogeneously distributed throughout the universe as an energy, it exerts a force,” Frieman said.

Both gravity and dark energy are affecting the large celestial bodies in the cosmos. What we are left with is “a cosmic tug of war,” Massey said.

“We have these different ideas,” Frieman said. “It could be dark energy. It could be something wrong with our idea of gravity. And so going forward we really want to figure out which of these things it is.”

“To do that, we need to carry out new surveys that are much more powerful than what has come before,” he said. “That means we need to build new instruments to carry out those surveys and that’s where the Dark Energy Survey comes in. We realized we wanted to carry out such a survey but that no existing facility could do it so we had to build one.”

An international collaboration of engineers and scientists contributed parts to build the massive camera that will be used to map one-eighth of the sky, giving a three-dimensional view of the stars.

The survey will take a census of 300 million galaxies in an effort to get a picture of how they clustered together in the early universe. The camera is gathering light that took billions of years to travel across space to the telescope in Chile.

“One of the things we’ll be doing is looking at how galaxies are distributed in space today, and then looking back in time billions of years into the past and seeing how that pattern of clustering has changed,” Frieman said. “That will tell us about this competition between dark energy and gravity.”

The Dark Energy Camera will also take images of 4,000 supernovae, bright dying stars that can still be seen at great distances as they explode.

"What we’ll do is use those observations of supernovae to measure how fast the expansion has been changing over time. Some kinds of dark energy would make the speed-up turn on more rapidly and other ideas it would maybe turn on more slowly. So what we really want to do is trace out how fast the universe is expanding as we look back in time several million years into the past,” Frieman said.

Installation of the camera onto the Blanco Telescope in Chile will be completed by August, when the aperture will open for the first time. “This camera, on the telescope that we’re going to put it on, will have the largest survey power of any camera in the world,” Frieman said. “So we will be able to make detailed and deep images over a larger part of the sky than anyone has been able to do before us.”