Now Complete, Telescope Instrument is Poised to Begin Its Search for Answers About Dark Energy

Even as the Dark Energy Spectroscopic Instrument, or DESI, lies dormant within a telescope dome on a mountaintop in Arizona, due to the COVID-19 pandemic, the DESI project has moved forward in reaching the final formal approval milestone prior to startup.

DESI is designed to gather the light of tens of millions of galaxies, and several million ultrabright deep-sky objects called quasars, using fiber-optic cables that are automatically positioned to point at 5,000 galaxies at a time by an orchestrated set of swiveling robots. The gathered light is measured by a group of 10 devices called spectrographs, which split the light into its spectrum, or separate colors.

Over the last few years students and technicians at the University of Michigan, under the leadership of physics professor Gregory Tarlé, built all the robotic fiber positioners for DESI. The team delivered a total of 7,300 positioners, including spares.

The measurements will help scientists map the universe in 3D and learn more about mysterious dark energy – which drives the universe’s accelerating expansion – and could also provide new insight about the life cycle of galaxies and about the cosmic web that connects matter in the universe.

Recently, Dr. Michael Schubnell, U-M research scientist, DESI Lead Observer and Focal Plane Scientist, wrapped up the commissioning portion of the DESI project for U-M Physics. He was responsible for the control electronics and software that allows the robots to move. He also worked with Lawrence Berkeley National Laboratory on testing the instrument subassemblies before shipment and again upon arrival at Kitt Peak.

Since late last year, an international team of DESI researchers, including Dr. Schubnell has been carrying out the commissioning of the DESI instrument, putting together all the components, testing the instrument on the sky and ensuring that it was capable of producing the science for which it was designed.

Project completion culminates 10-year effort by international team

After DESI passed a federal review in March, members of a federal advisory board formally approved the completion of the project on Monday, May 11. DESI was designed and built through the efforts of a large international collaboration that now numbers about 500 researchers at 75 institutions in 13 nations.

“Congratulations to the DESI team of U.S. and international labs and universities in developing this amazing, state-of-the-art spectroscopic instrument,” said Kathleen Turner, DESI program manager at the Department of Energy’s Office of High Energy Physics. “We are all looking forward to using DESI’s exquisite precision to map the expansion of the universe over time.”

Michael Levi, DESI project director and a scientist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is the lead institution in the project, said, “This is the culmination of 10 years of hard work by an incredibly dedicated and talented team, and a major accomplishment for all involved.”

He added, “We understand and appreciate the extraordinary privilege we have been given to work with this instrument – and even more so during this challenging time, as we continue as scientists to explore what lies beyond our world.”

“DESI is arguably the most sophisticated instrument ever placed on a telescope. It is a powerful new instrument for cosmology, and I am proud and excited to have reached this important milestone,” says physics Professor Gregory Tarlé and leader of the University of Michigan DESI project.

Preparing for a restart in DESI testing

In mid-March it became clear that a final testing phase of the instrument would be abruptly suspended due to the temporary shutdown of most activities at Kitt Peak National Observatory (KPNO), where DESI is located, to reduce the risk of spreading COVID-19.

Project participants moved quickly to capture a large, last batch of sky data during the March 14-15 weekend before the instrument was temporarily shuttered the following week, and that data proved useful in the project’s review for the construction completion milestone, known as Critical Decision 4, or CD-4.

In the months leading up to the temporary reduction in operations at KPNO, which is a Program of the National Science Foundation’s NOIRLab, researchers had engaged in DESI observing runs to troubleshoot technical snags and ensure its components are functioning properly.

Now, project participants say they are looking forward to a return to DESI testing in preparation for its startup and five-year mission.

“The early returns from the instrument were very gratifying after years of development,” said Daniel Eisenstein, a DESI spokesperson and Harvard University astronomy professor. “Now the whole team is eager to learn what DESI data will teach us about the Universe.”

Original written by Glenn Roberts Jr.

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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: www.desi.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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Gregory Tarlé