How Scientists Mapped Six Billion Years of Universe Expansion

Researchers involved in the Dark Energy Survey (DES) have published their most comprehensive depiction to date of the Universe's expansion over the past six billion years in Physical Research D. Employing an unparalleled array of cosmic measurements, this research enhances the accuracy of earlier DES studies twofold.

The results are largely in agreement with the standard model of cosmology, which is the most widely recognized theory regarding the Universe.

The international team of researchers, supported by the UK’s Science and Technologies Facilities Council (STFC) and six UK universities, is spearheaded by the Fermi National Accelerator Laboratory of the US Department of Energy.

A Century of Discovery

About a century ago, scientists observed that faraway galaxies seemed to be moving away from Earth. They determined that the greater a galaxy’s distance, the faster it recedes, offering the first crucial evidence that the Universe is expanding. Researchers initially anticipated that this expansion would decelerate over time due to gravitational forces.

However, in 1998, studies of distant supernovae indicated that the expansion of the Universe is accelerating instead of slowing down. Scientists introduced the concept of dark energy, which is currently believed to be responsible for the Universe's accelerated expansion.

Astrophysicists estimate that dark energy constitutes approximately 70 % of the mass-energy content of the Universe, yet its true nature remains one of the most profound enigmas in contemporary science.

Combining Four Cosmic Probes

The study integrates findings from 18 distinct research projects.

For the first time, it unifies four significant methodologies for investigating dark energy into one experiment, marking a milestone anticipated since the inception of DES 25 years ago.

The techniques are: weak gravitational lensing (distortions in galaxy shapes), galaxy clustering, supernovae, and galaxy clusters.

Intriguing Possibilities

It is exciting to see results from the full?DES?data set, more than 20 years after the project was first conceived. The sample of 140 million galaxies with shape measurements is phenomenal. While the headline results support a constant dark energy, future analyses will test the intriguing possibility of an evolving dark energy.

Ofer Lahav, Professor and Former Co-Chair, Committee and Chair, University College London, Dark Energy Survey (DES)

Far-Reaching Science

The DES collaboration conducted an extensive survey of the sky from 2013 to 2019 to investigate dark energy.

This survey utilized a specially designed 570-megapixel dark energy camera that was mounted on a telescope at the US National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile.

During the six-year period, scientists gathered images and data from hundreds of millions of distant galaxies, located billions of light-years away from Earth, effectively mapping approximately one-eighth of the sky.

For their most recent findings, researchers examined subtle distortions in the shapes of galaxies, referred to as weak gravitational lensing, to reconstruct the distribution of matter in the Universe over the last six billion years.

These measurements provide insights into how dark energy and dark matter have shaped the evolution of the Universe.

A Mystery Remains

The team evaluated their findings against two primary theories: one positing that dark energy is constant over time (the standard model of cosmology), and another suggesting that dark energy changes as the Universe expands.

DES discovered that while the data predominantly support the standard model, a persistent discrepancy exists regarding the clustering of matter in the Universe. This issue has become increasingly evident with the incorporation of the complete dataset.

International Collaboration

The DES represents a global partnership involving over 400 researchers from more than 35 institutions, with several participants hailing from the UK. The initiative is spearheaded by the Fermi National Accelerator Laboratory, which is part of the US Department of Energy.

Contributions from the UK to the most recent study encompass researchers from the University of Cambridge, the University College London, the University of Edinburgh, the University of Nottingham, the University of Portsmouth, and the University of Sussex.

Through STFC, the United Kingdom is additionally backing research initiatives that will enhance the efforts of the DES collaboration in the forthcoming generation of astronomical surveys. This encompasses the Vera C. Rubin Observatory, which is currently being constructed in Chile.

Solving Universal Mysteries

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.

Michele Dougherty, Executive Chair and Professor, Science and Technologies Facilities Council (STFC)

In the future, DES will integrate these recent discoveries with data from other dark energy experiments to investigate and evaluate alternative concepts regarding gravity and dark energy.

The study lays the foundation for potential advancements at the forthcoming Vera C. Rubin Observatory in Chile, which will conduct comparable studies through its Legacy Survey of Space and Time.