A new study using the Dark Energy Survey (DES) final datasets suggests potential inconsistencies in the standard cosmological model, known as ΛCDM. If confirmed, these findings could fundamentally alter our understanding of the universe.
DES was conducted using the 570-megapixel Department of Energy-fabricated Dark Energy Camera (DECam), mounted on the U.S. National Science Foundation Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF NOIRLab.
The ΛCDM (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 dark matter (25%) and dark energy (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 (DES), presented in a paper appearing on the arXiv preprint server and in talks at the American Physical Society’s Global Physics Summit 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 Fermi National Accelerator Laboratory. The DES was conducted using the 570-megapixel Department of Energy-fabricated Dark Energy Camera (DECam), mounted on the U.S. National Science Foundation (NSF) Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO) 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 supernova measurements, galaxy clustering analysis, and weak gravitational lensing, to study dark energy.
Two key DES measurements—Baryon Acoustic Oscillations (BAO) and distance measurements of exploding stars (Type Ia supernovae)—track the universe’s expansion history. BAO refers to a standard cosmic ruler 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 (CIEMAT) 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 most extensive and detailed supernova dataset 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.
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By integrating DES measurements with cosmic microwave background 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.”
The Dark Energy Camera (DECam), fabricated by the Department of Energy (DOE), is mounted on the Víctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in north-central Chile. Telescope construction started in 1969 with the casting of the primary mirror. The assembly at the Cerro Tololo mountaintop was finished in 1974. Upon completion of construction it was the 3rd largest telescope in the world, behind the 200-inch Hale telescope at Palomar Observatory in California and the BTA-6 in southern Russia, and was the largest in the Southern Hemisphere (a title that it held for 22 years). It was later named in 1995 in honor of Víctor M. Blanco, Puerto Rican astronomer and former director of CTIO. © DOE/FNAL/DECam/R. Hahn/CTIO/NOIRLab/NSF/AURA
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. Similar trends have emerged from other major cosmological projects, including the Dark Energy Spectroscopic Instrument (DESI), 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.
More information:
DES Collaboration, Dark Energy Survey: implications for cosmological expansion models from the final DES Baryon Acoustic Oscillation and Supernova data, arXiv (2025). DOI: 10.48550/arxiv.2503.06712
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National Science Foundation
Citation:
Latest dark energy survey data suggest possible variations in dark energy over time (2025, March 19)
