Sept. 12 was a red letter day for scientists eager to explore the mystery of dark energy — a kind of counter-force to gravity that is causing the expansion of our universe to speed up. That’s because the long-awaited Dark Energy Camera (DECam) achieved “first light,” producing its first pictures of the southern sky.
Nestled on a Chilean mountaintop, the better to take advantage of the region’s clear skies, the DECam is the culmination of an eight-year international effort on behalf of the Dark Every Survey (DES) — intended to be the largest galaxy survey yet undertaken, a successor to the hugely successful Sloan Digital Sky Survey.
While the DEC is still in the initial testing phase, once that is complete, the survey will begin in earnest. Over the next five years, astronomers will be able to detect light from eight billion years ago. The collaboration will compile high-resolution color images of fully one-eighth of the night sky, cataloging 300 million galaxies, 100,000 galaxy clusters, and 4000 supernovae.
There is much astronomers will be able to learn from such a detailed map, but chief among the objectives is combining four experimental probes of dark energy into a single experiment: galaxy clusters, supernovae, large-scale clumping of galaxies, and weak gravitational lensing.
“This will be the largest galaxy survey of its kind, and the galaxy shapes and positions will tell us a great deal about the nature of the physical process that we call dark energy, but do not currently understand,” Will Percival, a member of the DES collaboration and an astronomer at the University of Portsmouth, said via press release.
Scientists once believed the universe was in a steady state. But when Albert Einstein was working on his theory of general relativity in 1917, the math just didn’t add up: the universe should have been expanding.
So he invented something called the cosmological constant — a mathematical trick to balance everything out so that the equations described a static universe, rather than an expanding one.
But then astronomer Edwin Hubble discovered the universe actually was expanding — Einstein’s original equations were correct. Einstein dubbed the cosmological constant (lambda) his “greatest blunder.”
Apparently the universe likes to mess with us. In 1998, astronomers studying Type 1A supernovae discovered that the rate of expansion was accelerating due to an unknown force, dubbed dark energy. And one of the explanations for this effect is Einstein’s cosmological constant.
Further evidence in support of this hypothesis is mounting. Last May, a team of scientists from Swinburne University announced their independent confirmation of both the existence of dark energy and its rate of expansion, based on four years of data collected by a powerful spectrograph at the Australian Astronomical Observatory. And just a few weeks ago, a new, two-year study also concluded that dark energy is very real.
Yet there are still a few holdouts among cosmologists, some of whom argue there may be alternative explanations for this phenomenon, including modifications of Einstein’s theory of general relativity. Resolving this scientific dispute is one of the foremost challenges currently facing cosmologists.
With its array of 62 charged couple device (CCD) cameras, DECam is roughly the size of a phone booth, dwarfed by the vastness of the universe it surveys. But that might be just the thing scientists need to crack the dark energy enigma once and for all.
Images: (top) Zoomed-in image from the Dark Energy Camera of the barred spiral galaxy NGC 1365, in the Fornax cluster of galaxies. (bottom) Full Dark Energy Camera image of the Fornax cluster of galaxies. Credit: Dark Energy Survey Collaboration.