Eight billion years ago, rays of light from distant galaxies began their long journey to Earth. On Sept. 17, that ancient starlight found its way to a mountaintop in Chile, where the newly constructed Dark Energy Camera, the most powerful sky-mapping machine ever created, captured and recorded it for the first time.

That light may hold within it the answer to one of the biggest mysteries in physics — why the expansion of the universe is speeding up.

Scientists on the Dark Energy Survey collaboration announced this week that the Dark Energy Camera, the product of eight years of planning and construction by scientists, engineers and technicians on three continents, has achieved first light. A contingent of faculty, staff and students from the Department of Physics and Astronomy in the University of Pennsylvania’s School of Arts and Sciences is playing a major role in this collaboration.

“Back when the Survey was first proposed, there was a lot of skepticism we would ever be able to make measurements as subtle and precise as necessary for this project,” said Bhuvnesh Jain, professor of astrophysics and leader of the Penn team. “Now that the Dark Energy Camera is up and running, we are all very excited to begin examining the tremendous amount of data it will provide.”  

Other members of the team include department chair Larry Gladney, professor Gary Bernstein, associate professor Masao Sako and research-staff member Mike Jarvis. Their involvement in the Dark Energy Survey will represent their main research agenda for the next five years, as they have long tried to establish whether dark energy is the answer to one of largest outstanding questions in science: why is the expansion of the universe accelerating rather than slowing due to gravity?

“The achievement of first light through the Dark Energy Camera begins a significant new era in our exploration of the cosmic frontier,” said James Siegrist, the U.S. Department of Energy’s associate director of science for high energy physics. “The results of this survey will bring us closer to understanding the mystery of dark energy and what it means for the universe.”

“It is extremely satisfying to see the efforts of all the people involved in this project finally come together,” said Brenna Flaugher, project manager and scientist at Fermilab.

The Dark Energy Camera was constructed at the Department of Energy’s Fermi National Accelerator Laboratory in Batavia, Ill., and mounted on the Victor M. Blanco Telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory, which is the southern branch, located in Chile, of the U.S. National Optical Astronomy Observatory.

The Dark Energy Camera is the most powerful survey instrument of its kind; in a single snapshot it will see light from more than 100,000 galaxies up to 8 billion light years away. The camera’s array of 62 charged-coupled devices has an unprecedented sensitivity to very red light and, along with the Blanco Telescope’s large light-gathering mirror (which spans 13 feet across), will allow scientists from around the world to pursue investigations ranging from studies of asteroids in our own solar system to the understanding of the origins and the fate of the universe.

Penn’s involvement in the Survey began in 2006, when it developed new image-processing techniques that could deliver the subtle measurements necessary in the search for dark energy.  Armed with these techniques, scientists in the Dark Energy Survey collaboration will use the new camera to carry out the largest galaxy survey ever undertaken. They will use that data to carry out four probes of dark energy, studying galaxy clusters, supernovae, large-scale clumping of galaxies and weak gravitational lensing. This will be the first time all four of these methods will be possible in a single experiment.

Penn is at the helm of two of the four probes of dark energy. Jain is co-coordinator of the weak gravitational lensing group, and Sako is the co-coordinator of the supernova group.

Lensing is a phenomenon in which light from distant galaxies is bent by the gravity of massive objects on its way to Earth. Jain and Bernstein will compare hundreds of thousands of galaxies, looking for patterns in such distortions that would reveal dark energy at work. Jarvis is in charge of the Survey’s “lensing pipeline.” His work will reduce each of the galaxies imaged to their vital stats via computer algorithms.

As part of the supernovae group, Sako and Gladney will hunt for new stellar explosions and enlist the help of other telescopes to triangulate their positions, providing additional data about their home galaxies’ distance and motion. The massive scope of the Survey will enable the researchers to observe these relatively rare phenomena more regularly, but they will still have to act quickly to record data from the events before they fade from the sky.    

The Dark Energy Survey is expected to begin in December, after the camera is fully tested and Bernstein, co-leader of the Survey’s science-verification team, signs off on its accuracy.

“This camera, which is about the size of a Mini Cooper, needs to be aligned to five microns,” Bernstein said. “That’s less than a tenth of the width of a human hair.”  

Once operational, it will take advantage of the excellent atmospheric conditions in the Chilean Andes to deliver pictures with the sharpest resolution seen in such a wide-field astronomy survey.

Over five years, the survey will create detailed color images of one-eighth of the sky, or 5,000 square degrees, to discover and measure 300 million galaxies, 100,000 galaxy clusters and 4,000 supernovae.

“Every night is going to be an avalanche of data,” Jain said. “Our team will be scrambling to process these terabytes of images to discern the patterns produced by gravitational lensing.” 

The Dark Energy Survey is supported by funding from the Department of Energy; the National Science Foundation; funding agencies in Brazil, Germany, Spain and the United Kingdom; and the participating DES institutions.