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Scientists at the , have released  yet on how the Universe has expanded over the last six billion years.

The international group of researchers, with UK support from the  and six UK universities, including the , is led by the U.S. Department of Energy’s .

Combining multiple, independent measurements of the cosmos, the research doubles the precision of previous DES studies, while remaining broadly consistent with the standard model of cosmology, the most widely accepted theory of the Universe.

 combine results from 18 separate studies and, for the first time, bring together four major techniques for studying dark energy within a single experiment - a milestone envisioned when DES was conceived 25 years ago.

, Director of the ����������’s , said: "The beauty of the Dark Energy Survey has been bringing together several different types of observations of the cosmos, to learn about how the Universe expands. These results don't happen automatically - they're due to the hard work, joy and tears of hundreds of scientists, pressing forward together for 20 years."

The techniques include weak lensing and galaxy clustering which are two of the most powerful observational techniques in cosmology for studying the structure of the Universe and constraining cosmological parameters like dark matter and dark energy.

Weak lensing refers to the subtle distortion of light from distant galaxies as it passes through the gravitational fields of both dark and ordinary matter and produces small shape distortions that are only detectable statistically across many galaxies. Galaxy clustering measures how galaxies are distributed in space - specifically, how their positions are correlated with each other - and probes both the growth of structure over time and the geometry of the Universe.

The combination of techniques enabled scientists to cross-check their measurements and gain a more robust understanding of how the Universe behaves.

, Executive Chair, STFC, said: “This research shows the power of long-term international collaboration and UK investment in world-leading science. Dark energy remains one of the great unanswered questions in science. Studies like this demonstrate how bringing together different approaches can give us a clearer picture of our Universe and where future discoveries may lie.”

Far reaching science

To study dark energy, the  carried out a deep, wide-area survey of the sky between 2013 and 2019, using a specially constructed 570-megapixel Dark Energy Camera mounted on a telescope at the US National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile.

Over six years, scientists collected images and data from hundreds of millions of distant galaxies, billions of light-years from Earth, mapping about one-eighth of the sky.

By reconstructing the Universe’s matter distribution across six billion years, the measurements reveal how dark energy and dark matter have influenced the Universe’s evolution.

A mystery remains

The team compared their observations with two main theories, one in which dark energy remains constant over time (the standard model of cosmology), and another in which dark energy changes as the Universe evolves.

DES found that although the data mostly align with the standard model, broadly agreeing with the most widely accepted theory of the Universe, there remains a long-standing discrepancy in how matter clusters in the Universe, and this has become more pronounced with the inclusion of the full dataset.

A century of discovery

Around 100 years ago, scientists discovered that distant galaxies appeared to be moving away from Earth. They found that the further away a galaxy is, the faster it recedes, providing the first key evidence that the Universe is expanding.

Researchers initially expected that this expansion would slow down over time due to gravity. However, in 1998, observations of distant supernovae revealed that the Universe’s expansion is accelerating rather than slowing down.

To explain this surprising result, scientists proposed the idea of dark energy, which is now thought to drive the Universe’s accelerated expansion.

Astrophysicists believe dark energy makes up about 70 per cent of the mass-energy content of the Universe, yet we still know very little about it.

International collaboration

The Dark Energy Survey is an international collaboration of more than 400 astrophysicists, astronomers and cosmologists from over 35 institutions, spanning seven countries. Other UK contributions to the latest study, alongside the ����������, include researchers from:

• University of Cambridge
• University College London
• University of Edinburgh
• University of Nottingham
• University of Sussex

Through the STFC, the UK is also supporting research programmes that will advance the work of the DES collaboration in the next generation of astronomical surveys, including , currently under construction in Chile.

Paving the way

Looking ahead, DES will combine these latest findings with results from other dark energy experiments to explore and test alternative ideas about gravity and dark energy.

The work also helps prepare the ground for future breakthroughs at the upcoming  in Chile to do similar work with its .