Science News

5,000 Eyes to Capture the Colors of the Cosmos

Source: DESI Collaboration
Published on 28.10.2019


With installation near completion, DESI’s new sky-surveying instrument begins final testing. The latest milestone marks the opening of DESI’s final testing toward the formal start of observations in early 2020.

A new instrument mounted atop a telescope in Arizona has aimed its robotic array of 5,000 fiber-optic “eyes” at the night sky and captured the first images showing its unique view of galaxy light.It was the first test of the Dark Energy Spectroscopic Instrument, known as DESI, with its nearly complete complement of components. The long-awaited instrument is designed to explore the mystery ofdark energy, which makes up about 68 percent of the universe and is speeding upits expansion.

The Universe’s most detailed 3D map

DESI’s components are designed to automatically point at preselected sets of galaxies, gather their light, and then split that light into narrow bands of color to precisely map their distance from Earth and gauge how much the universe expanded as this light traveled to Earth. In ideal conditions, DESI can cycle through a new set of 5,000 galaxies every 20 minutes.

Gravity had slowed this rate of expansion in the early universe, though dark energy has since been responsible for speeding up its expansion. Like a powerful time machine, DESI will peer deeply into the universe’s infancy and early development – up to about 11 billion years ago – to create the most detailed 3-D map of the universe. By repeatedly mapping the distance to 35 million galaxies and 2.4 million quasars across one-third of the area ofthe sky over its five-year run, DESI will will provide very precise measurements of the universe’s expansion rate, and will also teach us more about dark energy. Quasars, among the brightest objects in the universe, allow DESI to look deeply into the Universe’s past.

DESI's focal area overlaps with the full moon light in the night sky. The 5.000 robotic eyes cover an area 38 times bigger than the full Moon. Each one of the robotic positioners can place an optical fiber in an object in order to trace its light (the red circle indicates the location of a single positioner). The light gathered of a tiny portion of the Triangulum Galaxy by one optical fiber is split up in a spectrum - below the image -, revealing the traces of the galaxy's components. This spectrum was gathered on October, 22nd. (C) Dustin Lang, Aaron Meisner, DESI Collaboration/Imagine Sky Viewer; NASA/JPL-Caltech/UCLA; and Legacy Surveys project.

“After a decade in planning and R&D, installation and assembly, we are delighted that DESI can soon begin its quest to unravel the mystery of dark energy,” said DESI Director Michael Levi of the Department of Energy’s Lawrence Berkeley National Laboratory, the lead institution for DESI’s construction and operations. "Most of the universe’s matter and energy are dark and unknown, and next-generation experiments like DESI are our best bet for unraveling these mysteries,” Levi added. “I am thrilled to see this new experiment come to life."

The Institute of Cosmos Sciences participates as a research Unit, led by ICREA professor Licia Verde. The team will analyze and interpret the upcoming observations during the next 5 years. Verde, recently awarded with the Catalonian National Research Award, says, “Is a fascinating moment for Cosmology because we are hoping to unveil the nature of the Universe’s components”. `La Caixa´ fellow researcher Héctor Gil-Marín explains, “DESI is going to see the Universe like no other instrument has been able to, so the precision will be maximum. We expect that the resulting information will be as unbiased,transparent and reliable as possible,” he emphasizes.

5.000 robotic “eyes”

Installation of DESI began in February 2018 at the Nicholas U. Mayall Telescope, at Kitt Peak National Observatory near Tucson, Arizona. Over the past 18 months, a bevy of DESI components were shipped to the site from institutions around the globe and installed on the telescope. “With DESI we are combining a modern instrument with a venerable old telescope to make a state-of-the-art survey machine.” said Lori Allen, director of the Kitt Peak National Observatory at the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory.

Among the early arrivals was an assembly of lenses packaged in a large steel barrel, together weighing in at three tons. Placed at the top of the telescope, DESI’s focal plane carries 5,000 robotic positioners that swivel in a choreographed “dance” individually focusing on galaxies. It also included a collection of spectrographs designed to split up the gathered light into three separate color bands, allowing precise distance measurements of the observed galaxies across a broad range of colors. These spectrographs measure redshift, which is a shift in the color of objects to longer, redder wavelengths due to the objects’ movement away from us. Redshiftis analogous to how the sound of a fire engine’s siren shifts to lower tones as it moves away from us.

“This is a very exciting moment,”said Nathalie Palanque-Delabrouille, a DESI spokesperson and an astrophysics researcher at France’s Atomic Energy Commission (CEA) who has participated inthe selection process to determine which galaxies and other objects DESI will observe. “This is a very significant advance compared to previous experiments. By looking at objects very far away from us, we can actually map the history of the universe and see its components by looking at very different objects from different eras" she said.

In words of Gregory Tarlé, a physics professor at the University of Michigan who led the student teams that assembled the robotic positioners for DESI and related components, “I want to find out what the nature of dark energy is,” he said. “We finally have a shot at really trying to understand the nature of this stuff that dominates the Universe.”.

DESI's full focal plane with the 5,000 robotic positioners. (C) DESI Collaboration

About DESI Collaboration

The DESI collaboration has participation from nearly 500 researchers at 75 institutions in 13 countries.

DESI is supported by the U.S.Department of Energy’s Office of Science; the U.S. National Science Foundation,Division of Astronomical Sciences under contract to the NSF’s National Optical-Infrared Astronomy Research

Laboratory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology of Mexico; the Ministry of Science, Innovation, and Universities of Spain; and DESI member institutions. The DESI scientists are honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation. View the full list of DESI collaborating institutions, and learn more about DESI here:

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