Dark energy: Can $40m camera help solve its mystery? (+video)

By measuring the spectra of a supernova, researchers can see how far the chemical fingerprints in the spectra have shifted toward the red end of the spectrum – a measurement that yields the pace at which the universe's expansion is carrying the supernova's host galaxy away from the observer.

Armed with distances and speeds, it's possible to take snapshots of the pace of expansion at various points in the past.

The problem: When they compared expansion rates from nearby supernova with those from distant ones, they discovered that somewhere along the way, the universe's expansion rate had been kicked up a notch. The earliest supernovae the teams picked up were 25 percent dimmer than they should have been.

Prior to the discovery of dark energy, cosmologists estimated that the universe had just enough matter and energy in it so that gravity would continue to slow the expansion, although the expansion rate would never reach zero.

In 2011, the discovery earned portions of a Nobel Prize in Physics for three researchers collectively representing both teams.

Researchers now say that several billion years ago, the universe had expanded to a point where gravity at the cosmic level became weak enough for dark energy – present from the beginning – to take over and speed the expansion.

The observation of an accelerating universe has drawn support from other, independent ways to observe the change. And it's overhauled the cosmos's recipe.

Prior to dark energy's discovery, some 5 to 10 percent of the universe was thought to consist of so-called baryonic matter – built from protons and neutrons. The rest was thought to consist of so-called dark matter, a form that astronomers couldn't directly detect but was inferred from its gravitational affects on galaxies and clusters of galaxies.

Now, the dominant ingredient appears to be dark energy, making up 74 percent of all the matter and energy in the cosmos. Twenty-two percent of the universe consists of dark matter, with baryonic matter – making up stars, planets, and people –filling out the remaining 4 percent.

The Dark Energy Camera is exquisitely sensitive to light at the red end of the spectrum, since at the distances the team is exploring, the expansion of the universe has reddened the light, in effect stretching it to longer wavelengths.

The Dark Energy Survey, which involves 120 scientists from five countries, will be interrogating several aspects of the cosmos for answers to researcher's questions about it, explains Dr. Frieman in an email exchange.

For instance, taking the measure of additional supernovae across time and space will refine estimates of how the pace of expansion has changed, he says.

In addition, over the past few billion years, the pace at which new clusters of galaxies are forming has slowed. Taking the measure of clusters at different points in the universe's history will allow scientists to estimate the pace of the construction slowdown, giving further insights into the nature of dark energy.

Other telescopes can peer farther back in time than the telescope that will gather light for the camera, but by nature they also cover far smaller patches of the sky.

"The very large area of our survey is necessary to get the information we want," Frieman says.

Among the Dark Energy Camera's "first light" images, taken Sept. 12, is a shot of a galaxy some 60 million light-years from Earth. The galaxy is a member of the Fornax cluster.

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