The UltraDeep Survey - The Nature of Dark Energy

Astronomers first realized the existence of dark energy when studying distant Type Ia supernovae - the powerful explosions of old, burnt-out white dwarf stars that have become too massive. They had made predictions of how bright distant supernovae should seem based on the standard model of the universe: galaxies were moving apart from each other at a constant speed, coasting along on the energy left over from the Big Bang. But when they analyzed the supernovae, they realized that the very distant ones seemed too faint. Could it be that galaxies weren't coasting, but rather moving apart ever faster and faster? Might some repulsive energy be causing the expansion of the universe to accelerate?

It was a controversial result. Some thought that there was no need to make up a new kind of energy - the supernovae might seem dim simply because dust was blocking their light. But shortly after the supernovae results, other scientists studying the cosmic microwave background - the glow left over from the Big Bang - found that some extra energy was necessary to explain the large-scale shape of the universe. Dark energy would fit the bill, and so now most astronomers agree that our universe is dominated by the mysterious stuff. Many theories have been made about the possible causes of dark energy, but the current supernova observations just aren't good enough to test the theories. We need more supernovae.

The CFHTLS UltraDeep Survey is going to give us just that. It will create the world's largest sample of supernova observations, taking high quality pictures of more than two thousand Type Ia supernovae. The supernovae will range from the relatively close-by - just 1.3 billion light years away - to some as distant as 8.2 billion light years away. (In redshift, that's a range of z = .1 to z = 1) With this many supernovae to examine, astronomers will be able to search for subtle patterns in the data that will allow them to choose between competing theories Their conclusions will give us the first precise measurement of the cause of dark energy.