Earth & Space

First results from DESI make the most precise measurement of our expanding universe

We now have the largest 3-D map of our cosmos ever created, thanks to DESI—a powerful instrument mounted atop a telescope in Arizona with a robotic array of 5,000 fiber-optic “eyes” that look into the night sky.

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The Dark Energy Spectroscopic Instrument (DESI) is mounted on the U.S. National Science Foundation Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory, a Program of NSF NOIRLab.

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We now have the largest 3-D map of our cosmos ever created, thanks to a powerful instrument mounted atop a telescope in Arizona with a robotic array of 5,000 fiber-optic “eyes” that look into the night sky. Over the last five years, the Dark Energy Spectroscopic Instrument—known in science circles as DESI—has measured the spectra of more than 30 million galaxies and 3 million quasars to determine how fast the universe expanded over 11 billion years.

DESI’s announcement today is the result of an ongoing international collaboration comprising more than 900 researchers from over 70 institutions, including astronomers at UC Santa Cruz with leadership roles in the project.

And yet, as big as this news is, they say it’s just the beginning.

“If the trends hinted here in this first-year dataset are confirmed in our Year Three analysis, this will be a major discovery,” said cosmologist Alexie Leauthaud, associate professor in UC Santa Cruz’s Astronomy and Astrophysics Department. “This is going to be a tremendously exciting time to be part of the DESI collaboration.”

Starting in July, Leauthaud will serve as a spokesperson for the effort—which entails lead-organizer duties—so she is perfectly positioned to provide updates. Other collaborating professors at UC Santa Cruz include Connie Rockosi and J. Xavier Prochaska, also in Astronomy & Astrophysics.

Rockosi led the commissioning of the instrument at the 4-meter Mayall telescope at Kitt Peak National Observatory, and her present role is as an instrument scientist, helping to keep it running in top shape. In addition, the professors credit “a phenomenal team” of UC Santa Cruz undergrads, grad students, and postdocs who have been deeply engaged with the project—visiting the telescope in Arizona on a regular basis to help with observations.

As explained in an announcement from Lawrence Berkeley National Laboratory, where DESI is based: “Understanding how our universe has evolved is tied to how it ends, and to one of the biggest mysteries in physics: dark energy, the unknown ingredient causing our universe to expand faster and faster.”

This is the first time scientists have measured the expansion history of the young universe with a precision better than 1%—giving us our best view yet of how the universe evolved. Researchers shared the analysis of their first year of collected data in multiple papers that will be posted today on the arXiv and in talks at the American Physical Society meeting in the United States and the Rencontres de Moriond in Italy.

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Last modified: Apr 12, 2025