Is dark energy changing? The mystery of cosmic expansion deepens

A recent study hints that the universe’s current model of cosmology, known as ΛCDM, might be facing inconsistencies. If confirmed, these results would introduce a need to fundamentally alter our understanding of cosmic dynamics.

The study leveraged the full dataset from the Dark Energy Survey (DES), which operates via the 570-megapixel Dark Energy Camera (DECam) developed by the U.S. Department of Energy. 

A changing view of the universe

Over the past several decades, modern cosmology has been guided by the ΛCDM framework. About 95% of the cosmos is attributed to elusive components – 25% to dark matter and 70% to dark energy – leaving just 5% as normal matter. 

Dark energy, in the form of a cosmological constant (Λ), has been seen as responsible for the accelerating expansion of space, holding a steady energy density. 

However, new findings from DES challenge that notion, suggesting that dark energy could be evolving over time. These findings join similar observations from other research efforts, adding weight to the speculation.

The DES collaboration unites more than 400 scientists from over 25 institutions, led by the U.S. Department of Energy’s Fermi National Accelerator Laboratory. 

Across six years – totaling 758 nights of observations – the project mapped nearly an eighth of the entire sky.

The researchers employed several methods, such as supernova surveys, galaxy clustering analyses, and weak gravitational lensing, aiming to illuminate dark energy’s role in cosmic expansion.

Tracing cosmic expansion

Two core DES methods – Baryon Acoustic Oscillations (BAO) and Type Ia supernova measurements – document the universe’s expansion pattern. BAO refers to a standardized cosmic scale imprinted by sound waves in the early universe, spanning around 500 million light-years. 

By measuring how these features stretch or shrink across cosmic history, astronomers can observe how dark energy changes the “standard ruler” over time.

“By analyzing 16 million galaxies, DES found that the measured BAO scale is actually 4% smaller than predicted by ΛCDM,” explained Santiago Avila of CIEMAT in Spain, who oversaw the BAO analysis for DES.

Supernovae of Type Ia act as “standard candles,” given that their intrinsic brightness is consistent enough for distance calculations, especially in concert with knowledge about their host galaxies. 

In 2024, DES released the largest Type Ia supernova dataset to date, providing refined measures of cosmic distances. When paired with BAO data, that updated supernova information backs up the anomalies seen in the 2024 results.

On the brink of a scientific revolution

By combining these DES observations with cosmic microwave background data, the research team inferred properties of dark energy and concluded that it might vary over time.

Should these findings hold, it would indicate that the cosmological constant is not truly constant, leading cosmologists to formulate new theoretical frameworks.

“This result is intriguing because it hints at physics beyond the standard model of cosmology,” said 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.”

Future research on dark energy

Although these results do not yet achieve definitive status, the researchers are set to incorporate other DES probes, such as galaxy clustering and weak lensing, to confirm or refine the present conclusions.

Comparable hints have emerged from other major cosmological projects, including the Dark Energy Spectroscopic Instrument (DESI), heightening the excitement among scientists.

“These results represent years of collaborative effort to extract cosmological insights from DES data,” commented 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.”

A final comprehensive DES analysis will combine additional cosmological methods to validate the findings and sharpen limits on dark energy. Many in the scientific community are waiting for these developments, as they may mark a shift in the way we view cosmic structure and expansion.

The Dark Energy Camera

The Dark Energy Camera was created by the Department of Energy and is mounted atop the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile. Construction of the telescope began in 1969 with the casting of its main mirror. 

Upon its 1974 completion, it was the world’s third-largest telescope, retaining the title of largest in the Southern Hemisphere for 22 years. It gained the name “Víctor M. Blanco” in 1995 in honor of the Puerto Rican astronomer and former CTIO director.

DECam is installed on the U.S t. National Science Foundation’s Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile – a Program of NSF’s NOIRLab.

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