Across the Universe
Stand outside under a dark sky. Look up. What do you see? If you’re lucky, you see stars. Maybe a few planets. Maybe the Moon. And, although you don’t know it, you’re also being bombarded by light from distant objects. Very very distant objects. Some of them are so far away that their light left on a cr0ss-cosmos journey billions of years ago.
That light tells a story about the objects that emitted it. But, it also tells a story about the rate at which the universe is expanding, as well as all the eons of history that occurred between the time the light left its source and got here to Earth for us to detect.
Eight billion years ago, rays of light from some distant galaxies began that journey. On September 12th, that ancient starlight found its way to a mountaintop in Chile. There, it was detected by a new type of camera — a powerful sky-mapping machine that is poised to give astronomers not just a look at some of the earliest galaxies in the history of the universe, but a clue to a mystery about why the expansion rate of the universe has been speeding up. It’s all part of a multi-year collaboration called the Dark Energy Survey.
The detector is called the Dark Energy Camera and its been mounted on the 4-meter Blanco Telescope in Chile. And, its first-light images are spectacular (you can read more about it and see more images at this link).
You can’t see Dark Energy among the galaxies of this image — it’s a process, not a thing. And, it’s quite a mysterious process. All astronomers know is that it has been playing a behind-the-scenes role in changing the rate at which the universe is spreading out. How it does this and why it started are two questions among many they hope to answer.
So, they have created this camera to probe the origin of the accelerating universe and help uncover the nature of dark energy. They plan to do this by measuring the 14-billion-year history of cosmic expansion with a degree of precision they’ve never had before, through a multi-year high-resolution galaxy survey.
Galaxy surveys are excellent ways to map the distribution of matter in the universe. Once you know where the matter is (and that includes the dark matter that is also there, but unseen), then you can get a better idea of how the matter is carried along by the expansion of the universe that began with the Big Bang nearly 14 billion years ago.
Specifically, this survey will probe for the existence of dark energy by studying galaxy clusters, assessing the large-scale clumping of galaxies, and measuring weak gravitational lensing. In addition, astronomers in the Dark Energy Survey C0llaboration (led by Fermilab in the U.S., and includes UCL (University College London), Portsmouth, Cambridge, Edinburgh, Sussex and Nottingham in the U.K.) will search out supernovae in distant galaxies and use their light to determine truly accurate distances to their galaxies. It’s not often you get so much data from a single experiment, and according to the scientists who planned the survey, it’s the first time all four of these methods will be possible in a single experiment. The galaxy shapes and positions it uncovers will reveal a lot of information about the nature of the physical process that astronomers call Dark Energy.
The full survey should begin in December, after the camera is fully tested. If the first images released this week are any indication, then astronomers will be in for a heck of a ride when the full survey is completed. The data should be incredible! 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. And, hopefully, at the end, when all is said and done, let’s hope astronomers have gotten at least a tiny inkling of the nature of this weird process called Dark Energy.
