Dark Energy Spectroscopic Instrument

After less than a year of data taking, DESI has already mapped out more galaxies than all previous 3D surveys combined — and it’s just getting started.

DESI will capture and study the light from tens of millions of galaxies and other distant objects to better understand our universe and the properties of dark energy. The formal start of DESI’s five-year survey follows a four-month trial run of its custom instrumentation that captured 4-million spectra of galaxies — more than the combined output of all previous spectroscopic surveys. Fermilab has contributed multiple components to the international collaboration led by Berkeley Lab.

Scientists have begun operating the Dark Energy Spectroscopic Instrument, or DESI, to create a 3-D map of over 30 million galaxies and quasars that will help them understand the nature of dark energy. The new instrument is the most advanced of its kind, with 5,000 robotic positioners that will enable scientists to gather more than 20 times more data than previous surveys. Researchers at Fermilab helped develop the software that will direct these positioners to focus on galaxies several billion light-years away and are currently in the process of fine-tuning the programs used before the last round of testing later this year.

The Dark Energy Spectroscopic Instrument, which will map millions of galaxies in 3-D, reaches final milestone toward its startup.

Berkeley Lab’s Dark Energy Spectroscopic Instrument aimed its robotic array of 5,000 fiber-optic “eyes” at the night sky Oct. 22 to capture the first images showing its unique view of galaxy light. It was the first test DESI with its nearly complete complement of components. Fermilab contributed key elements to DESI, including the corrector barrel, hexapod, cage and CCDs. Fermilab also provided the online databases used for data acquisition and the software for the instrument’s robotic positioners.

It took three sky surveys to prepare for a new project that will create the largest 3-D map of the universe’s galaxies and glean new insights about the universe’s accelerating expansion. This Dark Energy Spectroscopic Instrument project will explore this expansion, driven by a mysterious property known as dark energy, in great detail. The surveys, which wrapped up in March, have amassed images of more than 1 billion galaxies and are essential in selecting celestial objects to target with DESI, now under construction in Arizona.

From Berkeley Lab, Dec. 4, 2018: Key components of Berkeley Lab’s Dark Energy Spectroscopic Instrument are installed after months of planning, prep work. A team at Fermilab built the corrector, hexapod, and other top-end support structures. The structures are designed to align the lenses with an accuracy of tens of microns (millionths of a meter) – similar to the width of the thinnest human hair.

These international projects, selected during the process to plan the future of U.S. particle physics, are all set to come online within the next 10 years.

DESI, an instrument to help scientists get to the bottom of the dark energy mystery, is getting a little help from Fermilab.