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News — The  (Lambda-CDM) model has been the foundation of modern cosmology for some time now, successfully describing large-scale structures in the Universe. It proposes that 95% of the cosmos is composed of  (25%) and  (70%) — mysterious substances whose nature remains unknown. Only 5% of the Universe consists of ordinary matter.

Dark energy, represented by the cosmological constant (Λ), is thought to drive the accelerating expansion of the Universe, maintaining a constant energy density over time. However, new results from the Dark Energy Survey (), presented today in a  appearing on arXiv and in talks at the  in Anaheim, California, hint at a deviation from this assumption, suggesting that dark energy might evolve over time. These findings align with previous studies, reinforcing their significance.

The DES is an international collaboration comprising more than 400 scientists from over 25 institutions, led by the U.S. Department of Energy’s . The DES was conducted using the 570-megapixel Department of Energy-fabricated Dark Energy Camera (), mounted on the U.S. National Science Foundation (NSF)  at Cerro Tololo Inter-American Observatory () in Chile, a Program of NSF NOIRLab. By taking data on 758 nights across six years, DES scientists mapped an area almost one-eighth of the entire sky. The project employs multiple observational techniques, including  measurements,  analysis, and , to study dark energy.

Two key DES measurements — Baryon Acoustic Oscillations () and distance measurements of exploding stars () — track the Universe’s expansion history. BAO refers to a standard  formed by sound waves in the early Universe, with peaks spanning approximately 500 million light-years. Astronomers can measure these peaks across several periods of cosmic history to see how dark energy has stretched the scale over time.

Santiago Avila from the Centre for Energy, Environmental and Technological Research () in Spain, who was responsible for the BAO analysis in DES, says, “By analyzing 16 million galaxies, DES found that the measured BAO scale is actually 4% smaller than predicted by ΛCDM.”

Type Ia supernovae serve as 'standard candles', meaning they have a known intrinsic brightness. Therefore, their apparent brightness, combined with information about their host galaxies, allows scientists to make precise distance calculations. In 2024 DES published the  to date, providing highly accurate measurements of cosmic distances. These new findings from the combined supernovae and BAO data independently confirm the anomalies seen in the 2024 supernova data.

By integrating DES measurements with  data, researchers inferred the properties of dark energy — and the results suggest a time-evolving nature. If validated, this would imply that dark energy, the cosmological constant, is not constant after all, but a dynamic phenomenon requiring a new theoretical framework.

“This result is intriguing because it hints at physics beyond the standard model of cosmology,” says Juan Mena-Fernández of the Subatomic Physics and Cosmology Laboratory in Grenoble, France. “If further data support these findings, we may be on the brink of a scientific revolution.”

Although the current results are not yet definitive, upcoming analyses incorporating additional DES probes — such as galaxy clustering and weak lensing — could strengthen the evidence.  have emerged from other major cosmological projects, including the Dark Energy Spectroscopic Instrument (), raising anticipation within the scientific community .

“These results represent years of collaborative effort to extract cosmological insights from DES data,” says Jessie Muir of the University of Cincinnati. “There is still much to learn, and it will be exciting to see how our understanding evolves as new measurements become available.”

The final DES analysis, expected later this year, will incorporate additional cosmological probes to cross-check findings and refine constraints on dark energy. The scientific community eagerly awaits these results, as they could pave the way for a paradigm shift in cosmology.

Notes

[1] This  describes the DESI Collaboration’s analysis of the survey’s first three years of collected data, which also found hints of a time-evolving dark energy.

More information

These results are presented by the DES Collaboration.

, the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the  (a facility of , , , , , and ), NSF Kitt Peak National Observatory (), NSF Cerro Tololo Inter-American Observatory (), the Community Science and Data Center (), and NSF–DOE  (in cooperation with ’s  National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy () under a cooperative agreement with  and is headquartered in Tucson, Arizona. 

The scientific community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence of I’oligam Du’ag to the Tohono O’odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.

Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Funding Authority for Funding and Projects in Brazil, Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro, Brazilian National Council for Scientific and Technological Development and the Ministry of Science and Technology, the German Research Foundation and the collaborating institutions in the Dark Energy Survey.

Based in part on data acquired at the Anglo-Australian Telescope for the Dark Energy Survey by OzDES. We acknowledge the traditional custodians of the land on which the AAT stands, the Gamilaraay people, and pay our respects to elders past and present.

Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC. Visit Fermilab’s website at  and follow us on Twitter at .

The DOE 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 .

Links

Contacts

Santiago Avila
DES Collaboration scientist
Centre for Energy, Environmental and Technological Research
Email: [email protected]

Juan Mena-Fernández
DES Collaboration scientist
Grenoble Subatomic Physics and Cosmology Laboratory
Email: [email protected]

Jessie Muir
DES Collaboration scientist
University of Cincinnati
Email: [email protected]

Josie Fenske
Jr. Public Information Officer
NSF NOIRLab
Email: [email protected]

Fernando Torrecilla
Head of Communication, Outreach and Public Relations
Centre for Energy, Environmental and Technological Research
Email: [email protected]