The Lambda-CDM (ΛCDM) 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%). 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 hint at a deviation from this assumption, suggesting that dark energy might evolve over time.

The Dark Energy Survey (DES) was conducted using the 570-megapixel Department of Energy-fabricated Dark Energy Camera (DECam), mounted on NSF’s Víctor M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory, a Program of NSF NOIRLab.

By taking data on 758 nights across six years, the 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.

“By analyzing 16 million galaxies, DES found that the measured BAO scale is actually 4% smaller than predicted by ΛCDM,” said Dr. Santiago Avila, an astronomer at the Centre for Energy, Environmental and Technological Research (CIEMAT).

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, the DES team published the most extensive and detailed supernova dataset to date, providing highly accurate measurements of cosmic distances.

The new findings from the combined supernovae and BAO data independently confirm the anomalies seen in the 2024 supernova data.

By integrating the DES measurements with the Cosmic Microwave Background data, the 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,” said Dr. Juan Mena-Fernández, a researcher at the Subatomic Physics and Cosmology Laboratory.

“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.

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,” said Dr. Jessie Muir, a researcher at 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 team’s paper will be published in the journal Physical Review D.

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T.M.C. Abbott et al. (DES Collaboration). 2025. Dark Energy Survey: implications for cosmological expansion models from the final DES Baryon Acoustic Oscillation and Supernova data. Physical Review D, in press; arXiv: 2503.06712