The Dark Energy Spectroscopic Instrument (DESI) has made significant contributions to understanding the universe’s structure over the past 11 billion years, confirming Einstein’s theory of general relativity on a cosmic scale.
Through extensive data analysis of nearly 6 million galaxies and quasars, DESI has provided new insights into the growth of cosmic structures, the mass of neutrinos, and the distribution of dark matter and energy. As DESI continues to gather data, expectations are high for revealing more about the evolving nature of dark energy and the universe’s expansion.
Cosmic Growth and Gravity Testing With DESI
Gravity has shaped the cosmos we see today. Its pull transformed small differences in the amount of matter present in the early universe into the sprawling galaxy clusters and structures that fill space. A groundbreaking study using data from the Dark Energy Spectroscopic Instrument (DESI) has mapped the growth of this cosmic structure over the past 11 billion years, offering the most precise test of gravity on vast scales ever conducted.
DESI is a global effort involving over 900 researchers from more than 70 institutions, coordinated by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). This study confirmed that gravity behaves exactly as predicted by Einstein’s theory of general relativity, reinforcing the current model of the universe. These findings also place stricter limits on alternative theories of modified gravity, which scientists have explored to explain phenomena like the accelerating expansion of the universe, commonly linked to dark energy.
This simulation shows how more or less gravity affects the positions of galaxies that we observe, changing how they are clustered in a galaxy map. Because different models of gravity predict different clusterings of galaxies, DESI researchers can compare observations with simulations to test gravity at cosmic scales. Credit: Claire Lamman and Michael Rashkovetskyi / DESI collaboration
Verifying Einstein’s Theory at Cosmic Scales
“General relativity has been very well tested at the scale of solar systems, but we also needed to test that our assumption works at much larger scales,” said Pauline Zarrouk, a cosmologist at the French National Center for Scientific Research (CNRS) working at the Laboratory of Nuclear and High-Energy Physics (LPNHE), who co-led the new analysis. “Studying the rate at which galaxies formed lets us directly test our theories, and, so far, we’re lining up with what general relativity predicts at cosmological scales.”
The study also provided new upper limits on the mass of neutrinos, the only fundamental particles whose masses have not yet been precisely measured. Previous neutrino experiments found that the sum of the masses of the three types of neutrinos should be at least 0.059 eV/c2. (For comparison, an electron has a mass of about 511,000 eV/c2.) DESI’s results indicate that the sum should be less than 0.071 eV/c2, leaving a narrow window for neutrino masses.
Advanced Analysis Using DESI Data
The DESI collaboration shared their results in several papers posted to the online repository arXiv today. The complex analysis used nearly 6 million galaxies and quasars and lets researchers see up to 11 billion years into the past. With just one year of data, DESI has made the most precise overall measurement of the growth of structure, surpassing previous efforts that took decades to make.
Today’s results provide an extended analysis of DESI’s first year of data, which in April made the largest 3D map of our universe to date and revealed hints that dark energy might be evolving over time. The April results looked at a particular feature of how galaxies cluster known as baryon acoustic oscillations (BAO). The new analysis, called a “full-shape analysis,” broadens the scope to extract more information from the data, measuring how galaxies and matter are distributed on different scales throughout space. The study required months of additional work and cross-checks. Like the previous study, it used a technique to hide the result from the scientists until the end, mitigating any unconscious bias.
“Both our BAO results and the full-shape analysis are spectacular,” said Dragan Huterer, professor at the University of Michigan and co-lead of DESI’s group interpreting the cosmological data. “This is the first time that DESI has looked at the growth of cosmic structure. We’re showing a tremendous new ability to probe modified gravity and improve constraints on models of dark energy. And it’s only the tip of the iceberg.”
In this 360-degree video, take an interactive flight through millions of galaxies mapped using coordinate data from DESI. Credit: Fiske Planetarium, CU Boulder and DESI collaboration
Insights into Dark Matter and Future Prospects
DESI is a state-of-the-art instrument that can capture light from 5,000 galaxies simultaneously. It was constructed and is operated with funding from the DOE Office of Science. DESI is mounted on the U.S. National Science Foundation’s Nicholas U. Mayall 4-meter telescope at Kitt Peak National Observatory (a program of NSF NOIRLab). The experiment is now in its fourth of five years of surveying the sky and plans to collect roughly 40 million galaxies and quasars by the time the project ends.
The collaboration is currently analyzing the first three years of collected data and expects to present updated measurements of dark energy and the expansion history of our universe in spring 2025. DESI’s expanded results released today are consistent with the experiment’s earlier preference for an evolving dark energy, adding to the anticipation of the upcoming analysis.
“Dark matter makes up about a quarter of the universe, and dark energy makes up another 70 percent, and we don’t really know what either one is,” said Mark Maus, a PhD student at Berkeley Lab and UC Berkeley who worked on theory and validation modeling pipelines for the new analysis. “The idea that we can take pictures of the universe and tackle these big, fundamental questions is mind-blowing.”
DESI is supported by the DOE Office of Science 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; 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, Sciences, and Technologies of Mexico; the Ministry of Science and Innovation of Spain; and by the DESI member institutions.
The DESI collaboration is 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.
