Why is the universe expanding faster and faster? Catalan scientists are trying to figure it out.

GenevaThe universe is expanding faster and faster. But astronomers still don't know exactly why. Now the DES (Dark Energy Survey) collaboration has taken another step towards solving this enigma. For the first time have published results These measurements combine data from the two main sources available for measuring the expansion of the universe: the clustering of galaxies and how they deflect light through gravitational lensing. The analysis provides more precise estimates of the universe's composition and brings scientists closer to solving this puzzle.

"These results show how we can use diverse and complementary sources of information from the same observations," says Martin Crocce, associate research professor at the Institute of Space Sciences (ICE-CSIC) and coordinator of the analysis. "This is a very powerful tool, which allows us to obtain more precise and robust results," he emphasizes.

An expanding story

In 1929, the American astronomer Edwin Hubble determined that the most distant galaxies were receding from us at a greater speed. Hubble thus provided irrefutable proof that the universe is expanding, causing a paradigm shift in the understanding of the cosmos. Sixty years later, two independent teams demonstrated that the universe is not only expanding, but that it is doing so at an ever-increasing rate. This accelerated expansion still lacks a definitive explanation, although scientists believe it is caused by an energy that fills space called dark energy. It is currently estimated that dark energy makes up 70% of the universe's content.

To understand how dark energy works, the international Dark Energy Survey (DES) collaboration was created. This collaboration brings together more than 400 scientists from 25 institutions in seven countries, including the Institute for High Energy Physics (IFAE) and the ICE-CSIC, who have participated in the design, manufacture, testing, and installation of the detector that collects the measurements, as well as in the scientific analysis of the data.

A map of millions of galaxies

The new study compiles 18 separate projects using data from approximately 669 million galaxies located thousands of light-years from Earth. Over 758 nights across six years, astronomers collected data from a region equivalent to one-eighth of the entire sky. The published data analysis compares two theoretical cosmological models: the well-known Standard Model and an extended version in which dark energy evolves over time. The results appear to align better with the Standard Model, although astronomers cannot yet rule out the evolutionary model.

A groundbreaking finding is that both models show a significant discrepancy with previous studies when the distribution of matter in the universe is analyzed in detail. This discrepancy persists even when these data are combined with other experiments.

Furthermore, as proposed in the initial conception of the DES collaboration 25 years ago, the study also presents the first results obtained by combining the four different techniques available to determine dark energy: baryonic acoustic oscillations, type Ia supernovae, galaxy clusters, and the l

In the near future, the DES collaboration will combine the recently obtained results with measurements from other experiments to investigate and compare alternative cosmological models of gravity and dark energy. In this regard, the Rubin Observatory, an astronomical facility nearing completion on Cerro Pachón in northern Chile, will provide crucial information. "We have taken a significant step forward in the precision of the measurements, but all of these will improve considerably with new observations from the Rubin Observatory and other telescopes," explains Anna Porredon, a senior scientist at CIEMAT in Madrid, who is optimistic. "In 10 years we could have some answers about dark energy," she stated.

Mapping dark matter

Another study published in the journal Nature has presented a very high-definition map of the distribution of dark matter in the universe, which has a significant influence on the formation of the first structures, such as galaxies and galaxy clusters.

Thanks to observations made by the James Webb Space Telescope, researchers from Durham University in the UK, NASA's Jet Propulsion Laboratory, and the École Polytechnique Fédérale de Lausanne (EPFL) have taken a key step toward understanding the nature of this type of matter, which makes up 30% of the universe's content, and its origin. The study's authors conclude that these maps will be an important resource for future studies on galaxy formation and evolution, as well as the structure of the cosmos.