News from Ohio State University

First year of DESI results unveil new clues about dark energy

Researchers at The Ohio State University played a major role in analyzing the first year of data from the Dark Energy Spectroscopic Instrument’s survey into the history of the universe.

With 5,000 tiny robots in a mountaintop telescope, the Dark Energy Spectroscopic Instrument (DESI) collects and measures light from faraway space objects, granting scientists the ability to peer 11 billion years into the past. Studying how the cosmos evolved is important to understand how it began and might end, and opens up further questions about dark energy, an unknown ingredient causing our universe to expand faster and faster. 

To study dark energy’s effects over the last 11 billion years, DESI recently created the largest 3D map of the universe ever constructed, marking the first time that scientists have measured the expansion history of the universe in that early period. Such precise results have revealed unprecedented new hints about how the young universe might have evolved. Several members of the Ohio State DESI Team. From left to right, Erik Zaborowski, Chun-Hao To, Paul Martini, Peter Taylor, Klaus Honscheid, Andrei Cuceu and Ashley Ross.

DESI, an international collaboration involving more than 900 scientists from over 70 institutions around the world, is managed by the Department of Energy’s Lawrence Berkeley National Laboratory and includes large contributions from its Ohio State members. Led by physics professor Klaus Honscheid and astronomy and physics professor Paul Martini, the group now includes professors, research scientists, and graduate and undergraduate students from across the university.

Two Ohio State members, Andrei Cuceu, a postdoctoral fellow in astronomy and co-convener of the Lyman alpha science working group who led efforts to validate the instrument’s latest results, and Ashley Ross, a research scientist at the university’s Center for Cosmology and AstroParticle Physics and co-lead of the group that prepared DESI’s map for interpretation and accounted for changes in the instrument's performance, were integral to the recent DESI discoveries. 

“DESI looks at a wide range of times across the history of the universe and our work looked at some of those most distant measurements,” said Cuceu. “We did this by measuring a feature called baryon acoustic oscillations (BAO), minute ripple patterns that the universe provides that indicate the distribution of matter as it evolves.”

Large-scale surveys have used BAO measurements as cosmic rulers to map universe expansion in great detail, as researchers can get a better grasp of how dark energy may have stretched the universe at certain points and distances in time by comparing how they ripple through space. In a study led by Cuceu, one team used them to confirm the accuracy of 150 artificial datasets made to mimic DESI’s first data release, eventually concluding that the instrument’s findings were accurate throughout many different cosmological constraints. 

“We threw it at many different types of models and decisions across the analysis process, and it always seemed to generate roughly the same end result,” said Cuceu. Their findings are monumental because they show that DESI’s results provide tantalizing suggestions that call into question both typical models of cosmology and scientists’ current ideas about how physics works, said Ross.

One of the experiment’s goals is to essentially explore the nature of dark energy and if it changes over time,” he said. “These first DESI results offer a hint that it might not be a cosmological constant.”

 This artist’s rendering shows light from quasars passing through intergalactic clouds of hydrogen gas. Researchers can analyze the light to learn about distant cosmic structure. Credit: NOIRLab/NSF/AURA/P. Marenfeld and DESI collaborationDESI’s first research findings are presented throughout multiple papers, which can be found on the instrument’s data documentation site.

Beyond dark energy, DESI has also been used to study many other cosmological mysteries important for physics, such as the mass of important particles called neutrinos and how individual galaxies develop over time. Martini, who was the instrument scientist for DESI during its construction and commissioning, said that what makes DESI’s results so groundbreaking is the depth of the instrument’s analysis. 

“The improvement that we have managed to achieve is really driven not just by the fact that we have 10 times as much data as previous projects, but also that we took time to really understand the steps and potential sources of uncertainty much better,” Martini said.

As light from a distant quasar passes through gas in space, certain wavelengths of light are absorbed. Plotting the absorption lines reveals the “Lyman-alpha forest” (emphasized here in brown and green) and provides information about the distant clouds of gas between us and the quasar.  Credit: David Kirkby/DESI collaboration

This analysis covers data collected from 2021 to 2022, and DESI has been collecting new data ever since, meaning there are now three years of promising new data for scientists to comb through. 

“For now, we’re experimenting in a new era of cosmology,” said Cuceu. 

Toward the end of the decade, the data DESI continues to collect will also be used to complement next-generation sky surveys, such as the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope. As those instruments collect more precise data and scientists get to work decoding their results, many are confident that even more exciting pieces of the universe’s ever-changing cosmic puzzle will be revealed. 

“It is a really exciting result that could indicate a significant change in our understanding of the universe, and the fact that we see these hints about dark energy gives us fuel to keep going,” said Honscheid, who is the current DESI instrument scientist and instrument operations lead. “The future looks extremely bright for DESI and other long-term experiments like this one.”

​DESI is supported by the DOE Office of Science and by the National Energy Research Scientific Computing Center, a DOE Office of Science user facility. Additional support for DESI is provided by the U.S. National Science Foundation, the Science and Technology 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 and Innovation of Spain, and by the DESI member institutions. 

The DESI collaboration is honored to be permitted to conduct research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to Tohono O’odham Nation.