noirlab2512 — Science Release

Tantalizing Hints That Dark Energy is Evolving — New Results and Data Released by the DESI Project

Dark Energy Spectroscopic Instrument combines with other experiments to reveal signs of a time-varying dark energy

19 March 2025

The DESI collaboration has published a new analysis of dark energy using their first three years of collected data, which spans nearly 15 million galaxies and quasars. Combined with studies of the cosmic microwave background, supernovae, and weak lensing, the analysis hints that dark energy changes over time. Data Release 1, containing data from DESI’s survey validation and first year of observations, has now been made available for scientists and the public to explore.

The fate of the Universe hinges on the balance between matter and dark energy — the fundamental ingredient that drives its accelerating expansion. New results from the Dark Energy Spectroscopic Instrument (DESI) collaboration use the largest 3D map of our Universe ever made to track dark energy’s influence over the past 11 billion years. Researchers see hints that dark energy, widely thought to be a 'cosmological constant', might be evolving over time in unexpected ways.

DESI is an international experiment with more than 900 researchers from over 70 institutions around the world. DESI is managed by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (LBNL) with primary funding from the Department’s Office of Science. The instrument is mounted on the U.S. National Science Foundation Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory, a Program of NSF NOIRLab.

The collaboration shared their findings today in multiple papers that will be posted on the online repository arXiv and in a presentation at the American Physical Society’s Global Physics Summit in Anaheim, California.

“The Universe never ceases to amaze and surprise us,” says Arjun Dey, NOIRLab's DESI Project Scientist and Mid-Scale Observatories' Associate Director for Strategic Initiatives. “By revealing the evolving textures of the fabric of our Universe as never before, DESI and the Mayall telescope are changing our very understanding of the future of our Universe and nature itself.”

Taken alone, DESI’s data are consistent with our standard model of the Universe: Lambda CDM, where CDM is cold dark matter and lambda represents the simplest case of dark energy, where it acts as a cosmological constant. However, when paired with other measurements, there are mounting indications that the impact of dark energy may be weakening over time and that other models may be a better fit.

Those other measurements include the light leftover from the dawn of the Universe (the cosmic microwave background or CMB), distance measurements of exploding stars (supernovae), and observations of how light from distant galaxies is warped by the gravitational influence of dark matter (weak lensing).

So far, the preference for an evolving dark energy has not risen to '5 sigma' — the gold standard in physics that represents the commonly accepted threshold for a discovery. However, different combinations of DESI data with the CMB, weak lensing, and supernovae sets range from 2.8 to 4.2 sigma [1].

The analysis used a technique to hide the results from the scientists until the end, mitigating any unconscious bias about the data. This approach sets a new standard in how data from large spectroscopic surveys are analyzed.

DESI is a state-of-the-art instrument that can capture light from 5000 galaxies simultaneously, enabling it to conduct one of the most extensive surveys of the cosmos ever. The experiment is now in its fourth of five years surveying the sky, with plans to measure roughly 50 million galaxies and quasars (extremely distant yet bright objects with black holes at their cores) and more than 10 million stars by the time the project ends.

This shows a small fraction of the total DESI year-3 data in which the structure created by gravity is visible. This is the largest 3D map of the Universe ever made. Credit: DESI Collaboration/DOE/KPNO/NOIRLab/NSF/AURA/R. Proctor

The new analysis uses data from the first three years of observations and includes nearly 15 million of the best measured galaxies and quasars. It’s a major leap forward, improving the experiment’s precision with a dataset that is more than double what was used in DESI’s first analysis, which also hinted at an evolving dark energy.

DESI tracks dark energy’s influence by studying how matter is spread across the Universe. Events in the very early Universe left subtle patterns in how matter is distributed, a feature called Baryon Acoustic Oscillations (BAO). That BAO pattern acts as a standard ruler, with its size at different times directly affected by how the Universe was expanding. Measuring the ruler at different distances shows researchers the strength of dark energy throughout history. DESI’s precision with this approach is the best in the world.

The collaboration will soon begin work on additional analyses to extract even more information from the current dataset, and DESI will continue collecting data. Other experiments coming online over the next several years will also provide complementary datasets for future analyses.

“Our results are fertile ground for our theory colleagues as they look at new and existing models, and we’re excited to see what they come up with,” said Michael Levi, DESI director and a scientist at Berkeley Lab. “Whatever the nature of dark energy is, it will shape the future of our Universe. It’s pretty remarkable that we can look up at the sky with our telescopes and try to answer one of the biggest questions that humanity has ever asked.”

“These are remarkable results from an incredibly successful project,” says Chris Davis, NSF program director for NSF NOIRLab. “The potent combination of the NSF Mayall Telescope and DOE’s Dark Energy Spectroscopic Instrument shows the benefits of federal agencies working together on fundamental science that improves our understanding of the Universe.”

Alongside unveiling its latest dark energy results at the APS meeting today, the DESI collaboration also announced that its Data Release 1 (DR1) is now available for anyone to explore. The full set of DR1 files are available to access through the National Energy Research Scientific Computing Center (NERSC), a facility at Berkeley Lab where DESI processes and stores data. For additional convenience, the DR1 main catalogs and the full-depth spectra of DESI’s data release are made available as searchable databases via the Astro Data Lab and SPARCL at the Community Science and Data Center, a Program of NSF NOIRLab. These services are accessible to the entire astronomy community to facilitate data access and analysis. Space fans can also explore some of DESI’s data through an interactive portal: the Legacy Survey Sky Browser.

Stephanie Juneau, NSF NOIRLab astronomer, DESI Data team member, and the Project Scientist for SPARCL, says, “SPARCL provides the community with a user-friendly yet very powerful method to quickly access the spectra from a database, which can be much faster than reading files.”

The dataset is the largest of its kind, with information on 18.7 million objects — roughly 4 million stars, 13.1 million galaxies, and 1.6 million quasars (extremely bright but distant objects powered by supermassive black holes at their cores).

The new dataset vastly expands DESI’s Early Data Release (EDR), containing roughly 10 times as much data and covering seven times the area of sky. DR1 includes information from the first year of the 'main survey' collected between May 2021 and June 2022, as well as from the preceding five-month 'survey validation' where researchers tested the experiment.

“This new dataset being so large is exciting but it can be challenging to navigate this immense sea of data. So we prepared example tutorials that researchers and students can follow along,” says Juneau.

Although DR1 is just a fraction of what DESI will eventually produce, the 270-terabyte dataset represents a staggering amount of information, including precise distances to millions of galaxies. The release contains more than twice as many extragalactic objects (those found outside our galaxy) as have been collected in all previous 3D surveys combined.

Notes

[1] A statistical significance of 5 sigma means an almost certain likelihood that a result is not a statistical fluctuation. A 3-sigma event has a 0.3% chance of being a statistical fluke, but many 3-sigma events in physics have faded away with more data.

More information

This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences; the Science and Technology Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Humanities, Science and Technology of Mexico (CONAHCYT); the Ministry of Science, Innovation and Universities of Spain (MICIU/AEI/10.13039/501100011033), and by the DESI Member Institutions. The authors are honored to be permitted to conduct scientific research on I’oligam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation.

Current DESI Member Institutions include: Aix-Marseille University; Argonne National Laboratory; Barcelona-Madrid Regional Participation Group; Brookhaven National Laboratory; Boston University; Brazil Regional Participation Group; Carnegie Mellon University; CEA-IRFU, Saclay; China Participation Group; Cornell University; Durham University; École Polytechnique Fédérale de Lausanne; Eidgenössische Technische Hochschule, Zürich; Fermi National Accelerator Laboratory; Granada-Madrid-Tenerife Regional Participation Group; Harvard University; Kansas State University; Korea Astronomy and Space Science Institute; Korea Institute for Advanced Study; Lawrence Berkeley National Laboratory; Laboratoire de Physique Nucléaire et de Hautes Energies; Ludwig Maximilians University; Max Planck Institute; Mexico Regional Participation Group; National Taiwan University; New York University; NSF National Optical-Infrared Astronomy Research Laboratory; Ohio University; Perimeter Institute; Shanghai Jiao Tong University; Siena College; SLAC National Accelerator Laboratory; Southern Methodist University; Swinburne University; The Ohio State University; Universidad de los Andes; University of Arizona; University of Barcelona; University of California, Berkeley; University of California, Irvine; University of California, Santa Cruz; University College London; University of Florida; University of Michigan at Ann Arbor; University of Pennsylvania; University of Pittsburgh; University of Portsmouth; University of Queensland; University of Rochester; University of Toronto; University of Utah; University of Waterloo; University of Wyoming; University of Zurich; UK Regional Participation Group; Yale University. For more information, visit desi.lbl.gov.

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit http://www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

NSF NOIRLab, the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), NSF Kitt Peak National Observatory (KPNO), NSF Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona.

The scientific community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence of I’oligam Du’ag to the Tohono O’odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.

The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future. Please refer to www.nsf.gov.

Established in 2007 by Mark Heising and Elizabeth Simons, the Heising-Simons Foundation (www.heisingsimons.org) is dedicated to advancing sustainable solutions in the environment, supporting groundbreaking research in science, and enhancing the education of children.

The Gordon and Betty Moore Foundation, established in 2000, seeks to advance environmental conservation, patient care and scientific research. The Foundation’s Science Program aims to make a significant impact on the development of provocative, transformative scientific research, and increase knowledge in emerging fields. For more information, visit www.moore.org.

The Science and Technology Facilities Council (STFC) of the United Kingdom coordinates research on some of the most significant challenges facing society, such as future energy needs, monitoring and understanding climate change, and global security. It offers grants and support in particle physics, astronomy and nuclear physics, visit www.stfc.ac.uk.