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The Dark Energy Camera photographs galaxies from its perch on the Blanco telescope in Chile.
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High in the Chilean Andes, a massive project to probe the nature of dark energy has begun.
The Dark Energy Survey (DES) launched on 31 August at the 4-metre Blanco telescope at the Cerro Tololo Inter-American Observatory. It is one of several new pushes to explore the physical properties of dark energy, the mysterious force that is driving the universe to expand at an ever-faster rate.
Over the course of five years, the DES will map 300 million galaxies over one-eighth of the night sky. Its backbone is a 570-megapixel digital camera (pictured, right), designed to capture sharp images of galaxies and galaxy clusters. Such high resolution is essential because the DES measures weak gravitational lensing, the phenomenon in which light from distant cosmic objects is subtly distorted by the gravity of matter between them and Earth.
Weak lensing can be hard to spot. A competing Japanese-led survey, which uses the Hyper Suprime-Cam in Hawaii, relies on an even more detailed, 870-megapixel camera. That camera is mounted on a larger machine, the 8.2-metre Subaru telescope, and so it can image fainter galaxies than the DES can. The DES covers more area on the sky, however. Both surveys aim to measure enough weak lensing to map matter across the universe — a three-dimensional web that can reveal the fingerprints of dark energy through time.
Along with weak lensing, the DES has a couple of other tools in its arsenal. To beef up the matter map, it will count galaxy clusters at different distances from Earth. And it will probe for distant supernovae, whose otherwise reference light is dimmed as the universe expands. This technique was originally used to discover the accelerating cosmic expansion, and netted its scientists the 2011 Nobel Prize in physics.
The DES also hopes to muscle in on the territory of studying sound waves in the early universe. Its sky maps could reveal the effects of pressure waves frozen in place some 370,000 years after the big bang. Those results, in turn, could shed light on how the expansion rate of the universe changed over time, presumably driven by dark energy.
But other approaches have a head start in this arena. The ongoing BOSS survey and its planned successor, BigBOSS, focus on taking spectra of these acoustic waves, known as baryon acoustic oscillations. BOSS has already mapped these cosmic ripples and provided some of the tightest constraints on dark energy through time.
Quelle: nature-news
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Blanco-4M
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Why is the universe speeding up?
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In 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. Yet, according to Einstein's theory of General Relativity, gravity should lead to a slowing of the expansion. To explain cosmic acceleration, cosmologists are faced with two possibilities: Either 75% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.
The Dark Energy Survey (DES) is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. This collaboration is building an extremely sensitive 570-Megapixel digital camera, DECam, and will mount it on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory high in the Chilean Andes. Starting in Sept. 2012 and continuing for five years, DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.
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Dark Energy Survey begins five-year mission to map southern sky in tremendous detail
Tonight, as the sun sinks below the horizon, the world’s most powerful digital camera will once again turn its gleaming eye skyward. Tonight, and for hundreds of nights over the next five years, a team of physicists and astronomers from around the globe will use this remarkable machine to try to answer some of the most fundamental questions about our universe.
On Aug. 31, the Dark Energy Survey (DES) officially began. Scientists on the survey team will systematically map one-eighth of the sky (5000 square degrees) in unprecedented detail. The start of the survey is the culmination of 10 years of planning, building and testing by scientists from 25 institutions in six countries.
The survey’s goal is to find out why the expansion of the universe is speeding up, instead of slowing down due to gravity, and to probe the mystery of dark energy, the force believed to be causing that acceleration.
“The Dark Energy Survey will explore some of the most important questions about our existence,” said James Siegrist, associate director for High Energy Physics at the U.S. Department of Energy’s Office of Science. “In five years’ time, we will be far closer to the answers, and far richer in our knowledge of the universe.”
“With the start of the survey, the work of more than 200 collaborators is coming to fruition,” said DES Director Josh Frieman of the U.S. Department of Energy’s Fermi National Accelerator Laboratory. “It’s an exciting time in cosmology, when we can use observations of the distant universe to tell us about the fundamental nature of matter, energy, space and time.”
The main tool of the survey is the Dark Energy Camera, a 570-megapixel digital camera built at Fermilab in Batavia, Ill., and mounted on the 4-meter Victor M. Blanco telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in the Andes Mountains in Chile. The camera includes five precisely shaped lenses, the largest nearly a yard across, that together provide sharp images over its entire field of view.
The Dark Energy Camera is the most powerful survey instrument of its kind, able to see light from more than 100,000 galaxies up to 8 billion light-years away in each snapshot.
“The start of the Dark Energy Survey is an important milestone,” said CTIO Director Nicole van der Bliek. “The Dark Energy Camera, in conjunction with the Blanco telescope here at CTIO, will greatly increase our understanding of the forces that control the expansion of our universe.”
Over five years, the survey will obtain color images of 300 million galaxies and 100,000 galaxy clusters and will discover 4,000 new supernovae, many of which were formed when the universe was half its current size. The data collected will be processed at the National Center for Supercomputing Applications (NCSA) at the University of Illinois in Urbana and then delivered to collaboration scientists and the public.
“NCSA is pleased to be producing and distributing the refined data products that will enable this science,” said Don Petravick, principal investigator of the DES Data Management Operation.
The survey’s observations will not be able to see dark energy directly. However, by studying the expansion of the universe and the growth of large-scale structure over time, the survey will give scientists the most precise measurements to date of the properties of dark energy.
“We’re looking at this big galaxy map of the universe as a way of finding evidence for dark energy and characterizing its nature with cosmic epoch,” said Ofer Lahav of University College London and head of the DES Science Committee. “An even more challenging goal for DES is to tell if what causes the acceleration of the universe is indeed dark energy, or something entirely different."
The survey will use four methods to probe dark energy:
Counting galaxy clusters. While gravity pulls mass together to form galaxies, dark energy pulls it apart. The Dark Energy Camera will see light from 100,000 galaxy clusters billions of light-years away. Counting the number of galaxy clusters at different points in time sheds light on this cosmic competition between gravity and dark energy.
Measuring supernovae. A supernova is a star that explodes and becomes as bright as an entire galaxy of billions of stars. By measuring how bright they appear on Earth, we can tell how far away they are. Scientists can use this information to determine how fast the universe has been expanding since the star’s explosion. The survey will discover 4000 of these supernovae, which exploded billions of years ago in galaxies billions of light-years away.
Studying the bending of light. When light from distant galaxies encounters dark matter in space, it bends around the matter, causing those galaxies to appear distorted in telescope images. The survey will measure the shapes of 200 million galaxies, revealing the cosmic tug of war between gravity and dark energy in shaping the lumps of dark matter throughout space.
Using sound waves to create a large-scale map of expansion over time. When the universe was less than 400,000 years old, the interplay between matter and light set off a series of sound waves traveling at nearly two-thirds the speed of light. Those waves left an imprint on how galaxies are distributed throughout the universe. The survey will measure the positions in space of 300 million galaxies to find this imprint and use it to infer the history of cosmic expansion.
The Dark Energy Survey is supported by funding from the U.S. Department of Energy Office of Science; the National Science Foundation; funding agencies in the United Kingdom, Spain, Brazil, Germany and Switzerland; and the participating institutions.
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DECam
The Dark Energy Survey officially began on Aug. 31. Using the powerful Dark Energy Camera, scientists will map a portion of the sky in unprecedented detail, seeking answers to the mystery of dark energy.
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Composite DECam image (combining images from 4 filters) of the cluster of galaxies RXJ 2248-4431. Bright points with horizontal white lines are stars in our own galaxy.
Quelle: DES
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