In 1998, scientists studying a supernovae discovered that the expansion of the universe was actually accelerating, not expanding at a steady rate as had been believed since the 1920’s. To explain this odd phenomenon, the scientists proposed that a force, called “dark energy” was driving the expansion. Dark energy competes with gravity. Rather than pulling things together as gravity does, dark energy pushes them apart. And the strange stuff was estimated to make up a whopping three-quarters of our universe (with the similarly weird “dark matter” making up 23% and normal stuff comprising the remaining 4%). Scientists think dark energy may be the mysterious cosmological constant that Einstein was working on (and eventually gave up on) with his theory of general relativity and they aim to find out why the universe is expanding faster, rather than slowing down as gravity does its thing.
Joshua Frieman, director of the Dark Energy Survey (DES) explains:
“In the early universe we think gravity was the dominant force, that the universe was slowing down, and galaxies were forming. But in the last few billion years we think dark energy has taken over from gravity, sped up the cosmic expansion, and slowed down the formation of new galaxies.”
Like gravity, we don’t have a very good grasp on the concept and since the discovery of dark energy, there hasn’t really been a good instrument by which to explore this phenomena. The Dark Energy Camera (DECam) intends to solve the question of dark energy once and for all.
Since dark energy cannot be seen or measured, astronomers study its effect on other astronomical bodies. DECam, which can peer 8 billion years into space, will provide astronomers with a map that allows them to see cosmic expansion back to 8 billion years ago. They will be able to compare how the universe is expanding now to how it was expanding 8 billion years ago. Frieman explained how DECam will work:
“What the Dark Energy Survey is designed to do is to make a map of about 300 million galaxies. Then in a separate survey we will make a kind of cosmic movie–we’ll go back to the same part of the sky every few nights and measure about 4,000 supernovae. And by making such a large map and measuring these supernovae, we plan to probe the properties of dark energy with much greater precision than we’ve been able to do with previous surveys and previous data.”
One of the problems astronomers encounter when studying dark energy is a facet of light related to objects that are moving away from us. They shift into the red and infrared bands of the light spectrum. The redshift characteristic is a problem since normal cameras are great at capturing light in the blue range, but they are not so good at capturing light in the required red range.
“We want to look deep into the past of the universe, and as we look further and further outward, further back into the past, we’re seeing galaxies that are receding away from us faster and faster with the expansion of the universe. A galaxy that’s moving away from us rapidly, its light will be shifted from the blue into the red part of the visible spectrum simply due to the fact that it’s moving away from us at a very high speed.”
To solve this problem, DECam was constructed so that the camera’s 62 charge-coupled devices (CCDs) would be more sensitive to red-shifted light. This is the primary factor that makes DECam uniquely equipped to study dark energy.
The phone-booth sized Dark Energy Camera took eight years to construct. It was installed on the 4m Victor M. Blanco telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory (CTIO) in Chile. It was constructed with a very wide field of view rather than the classic narrow field of view seen with typical telescope devices. This allows DECam to survey one-eighth of the sky in the 522 days it will be imaging for the Dark Matter Survey.
Over the course of five years, beginning in December 2012, DECam will survey one-eighth of the sky (20 times larger than the full moon), image more than 300 million galaxies, 100,000 galaxy clusters, and 4,000 supernovae, the bright dying throes of stars.
You can follow the Dark Energy Survey project on their website and check out a sample of their photo gallery below.