Gravity has shaped our cosmos. Its attractive influence turned tiny differences in the amount of matter present in the early universe into the sprawling strands of galaxies we see today. A new study using data from the Dark Energy Spectroscopic Instrument (DESI) has traced how this cosmic structure grew over the past 11 billion years, providing the most precise test to date of gravity at very large scales.
DESI is an international collaboration of more than 900 researchers from over 70 institutions around the world and is managed by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). In their new study, DESI researchers found that gravity behaves as predicted by Einstein’s theory of general relativity. The result validates our leading model of the universe and limits possible theories of modified gravity, which have been proposed as alternative ways to explain unexpected observations – including the accelerating expansion of our universe that is typically attributed to dark energy.
"These data allow us to study how fast the largest structures of the universe have formed, and thus set limits in the Einstein General Relativity theory at cosmological scales, much larger than the solar system scales" explains Héctor Gil Marín from the Institute of Cosmos Sciences of the University of Barcelona and member of the Institute of Space Studies of Catalonia who has co-lead this new analysis. "So far the results perfectly fit the predictions by the Einstein General Relativity Theory".
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 clustering of galaxies, DESI researchers can compare observations with simulations to test gravity at cosmic scales.
Credit: Claire Lamman and Michael Rashkovetskyi / DESI collaboration
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.
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.
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
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.
«The results of the first year of DESI data are stunning», says Eusebio Sánchez, a researcher at CIEMAT who has contributed to the data analysis. «And this is only the beginning, the project is taking more data that will allow us to improve a lot the current understanding of gravity and dark energy».
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 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.
«The distribution of galaxies suggests the presence of dark matter and dark energy, both of which remain largely mysterious to us», says Hui Kong, a postdoctoral researcher at IFAE who worked on the curation of the galaxy catalogs. «However, the precise measurements provided by DESI offer promising insights into these fundamental questions about the universe».
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.
The institutions participating in DESI include the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), the Instituto de Ciencias del Espacio (ICE-CSIC/IEEC), the Institut de Ciències del Cosmos at the Universitat de Barcelona (ICCUB), the Institut de Física d'Altes Energies (IFAE), the Instituto de Física Teórica (IFT-UAM/CSIC), the Instituto de Astrofísica de Andalucía (IAA) and the Instituto de Astrofísica de Canarias (IAC).
The full list of participating institutions and more information about DESI is available at: [https://www.desi.lbl.gov](https://www.desi.lbl.gov).
