for National Geographic News
A new color-coded image represents the first visual evidence of the existence of dark energy, a mysterious force that astronomers think is causing the expansion of the universe to speed up.
"This is the first time when we actually see the effect of dark energy in a picture," said study leader István Szapudi of the University of Hawaii. "This is the most direct evidence of dark energy."
(Related: "At Ten, Dark Energy 'Most Profound Problem' in Physics" [May 16, 2008].)
The new image reveals the spectral fingerprints created by dark energy as it stretches huge supervoids and superclusters, structures that are roughly half a billion light-years across.
Superclusters are filled with dense clusters of galaxies, while supervoids are made up of mostly empty space.
According to the team, there is only a 1-in-200,000 chance that their detection of dark energy's fingerprints happened randomly.
Hot and Cold
Using mapping data gathered by the Sloan Digital Sky Survey, the team found evidence that dark energy alters ancient microwave radiation as it passes through superclusters and supervoids.
This diffuse radiation, called the cosmic microwave background, is the faint buzz of microwaves left over after the big bang.
Theory had predicted that as the universe expands at a constant rate, microwaves should gain energy as they enter a supercluster and lose an equal amount of energy as they leave.
The reverse should happen as microwaves travel through supervoids.
But if dark energy is causing the universe's expansion to accelerate, superclusters and supervoids should flatten out over time relative to the radiation.
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