On April 14, the 5,000 fiber-optic eyes of the Dark Energy Spectroscopic Instrument, or DESI, swiveled onto a patch of sky near the Little Dipper. Roughly every 20 minutes, they locked on to distant pinpricks of light, gathering photons that had traveled toward Earth for billions of years.

When the sun rose, collaborators from institutions around the world, including the University of Michigan, marked completion of a major milestone: successfully surveying all of the area in DESI’s originally planned map of the universe.

The five-year survey, finished ahead of schedule and with vastly more data than expected, has produced the largest high-resolution 3D map of the universe ever made. Researchers use that map to explore dark energy, the fundamental ingredient that makes up about 70% of our universe and is driving its accelerating expansion.

By comparing how galaxies clustered in the past with their distribution today, researchers have traced dark energy’s influence over 11 billion years of cosmic history. Surprising results using DESI’s first three years of data hinted that dark energy, once thought to be a “cosmological constant,” might be evolving over time.

With the full set of five years of data, researchers will have significantly more information to test whether that hint disappears or grows. If confirmed, it would mark a major shift in how we think about our universe and its potential fate, which hinges on the balance between matter and dark energy.

“The stunning discovery by DESI that dark energy is likely dynamic, has forced us to rethink everything we thought we understood about the nature of dark energy and its origin,” said Gregory Tarlé, U-M emeritus professor of physics. “We are now considering models of dark energy and its association with the formation of stars and black holes that were unthinkable when we first started construction.”

You may read more of this article at the Michigan News website. Also see the Michigan Physics video about our students and technicians making components for DESI on the same website.

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Camille Avestruz
Dragan Huterer
Michael Schubnell
Gregory Tarlé