Department of Energy

The Next Dimension of Mapping the Universe: The Dark Energy Spectroscopic Instrument

June 11, 2015

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Zoomed-in image from the Dark Energy Camera of the barred spiral galaxy NGC 1365, in the Fornax cluster of galaxies, which lies about 60 million light years from Earth -- in other words, far, far away. | Photo courtesy of the Dark Energy Survey Collaboration.

Zoomed-in image from the Dark Energy Camera of the barred spiral galaxy NGC 1365, in the Fornax cluster of galaxies, which lies about 60 million light years from Earth -- in other words, far, far away. | Photo courtesy of the Dark Energy Survey Collaboration.

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Dark energy remains one of science’s great mysteries. Scientists believe it makes up about 70 percent of the universe and is causing an acceleration in the expansion of the universe, but what it is and how it works are still unknown.

Scientists at the Energy Department’s National Labs are working to change that.

Last year, I wrote about the Dark Energy Camera, or DECam -- the world’s most powerful digital camera, located atop a telescope in Chile -- which was entering its second year of surveying the skies to study the effects of dark energy. And while two-dimensional data from the DECam’s second survey is currently being analyzed, many of the scientists who work on DECam have set their sights on another dimension: the third.

These scientists are developing the Dark Energy Spectroscopic Instrument, or DESI, which will create the largest 3-D map of the universe ever made. Once completed, DESI will be placed atop a telescope similar to the one used for DECam -- the Mayall four-meter telescope in Arizona -- to capture five years of data. This will produce a map of the northern sky spanning 11 billion light-years and measuring about 25 million galaxies and quasars, all the way back to when the universe was 2 billion years old.

It will do this by collecting light using optical fibers that look through the instrument's lenses and can be wiggled around to point precisely at galaxies. With 5,000 fibers, it can collect light from 5,000 galaxies at a time. These fibers will pass the galaxy light to a spectrograph -- an instrument that measures how much light the galaxies produce at each wavelength -- and researchers will use this information to precisely determine each galaxy's three-dimensional position in the universe.

Fermilab and Lawrence Berkeley National Lab are collaborating on the project, which is expected to see first light in 2019.