How gravity behaves at cosmic scales explained by DESI

New results from the Dark Energy Spectroscopic Instrument (DESI) reveal how galaxies cluster throughout cosmic history, aligning with Einstein’s general theory of relativity.

Researchers have utilized the Dark Energy Spectroscopic Instrument (DESI) to map nearly six million galaxies across 11 billion years of cosmic history, allowing them to study the clustering of galaxies over time and investigate the growth of cosmic structure. This analysis of DESI’s first-year data provides one of the most stringent tests to date of Einstein’s general theory of relativity.

Photo credit: KPNO/NOIRLab/NSF/AURA/R.T. Sparks

DESI provides best test yet of how gravity behaves at cosmic scales

Gravity has shaped the cosmos, turning tiny variations in the early Universe’s matter into the vast cosmic structures seen today. A new study based on DESI’s first year of data traces how this structure has grown over the past 11 billion years, providing the most precise test yet of gravity’s behavior at large scales.

DESI is a state-of-the-art instrument capable of capturing light from 5,000 galaxies simultaneously. It was constructed and is operated with funding from the Department of Energy’s 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 program is in its fourth year of a five-year survey and is set to observe approximately 40 million galaxies and quasars by its conclusion.

The DESI project is an international collaboration involving over 900 researchers from more than 70 institutions worldwide and is managed by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).

In the latest study, DESI researchers found that gravity behaves as predicted by Einstein’s general theory of relativity. This result validates the leading model of the Universe and limits possible theories of modified gravity, which have been proposed as alternatives to explain unexpected phenomena, such as the accelerating expansion of the Universe typically attributed to dark energy.

The DESI collaboration shared these findings in several papers posted to the online repository arXiv. The complex analysis used nearly six million galaxies and quasars, enabling researchers to peer 11 billion years into the past. With just one year of data, DESI has made the most precise overall measurement of the growth of cosmic structure, surpassing previous efforts that took decades to complete.

These results extend the analysis from DESI’s first-year data, which in April made the largest 3D map of the Universe to date and hinted that dark energy might be evolving over time. The April results focused on baryon acoustic oscillations (BAO) in galaxy clustering, while the new analysis broadens the scope to measure galaxy and matter distribution on various scales across space. The study also provides more accurate constraints on the mass of neutrinos, the only fundamental particles whose masses have not been precisely measured. Although neutrinos slightly influence galaxy clustering patterns, the quality of DESI’s data allows these effects to be measured, providing the most stringent constraints to date, complementing laboratory measurements.

DESI Observing

The study involved months of additional work and cross-checks. To minimize unconscious bias, the scientists used a technique to hide results until the end of the analysis.

Photo credit: KPNO/NOIRLab/NSF/AURA/T. Slovinský

“This research is part of one of the key projects of the DESI experiment — to explore the fundamental aspects of our Universe at large scales, such as the distribution of matter, the behavior of dark energy, and the properties of fundamental particles,” said Stephanie Juneau, an NSF NOIRLab astronomer and a member of the DESI collaboration. “By comparing the evolution of matter distribution in the Universe with existing predictions, including Einstein’s general relativity and competing theories, we are refining our models of gravity.”

The collaboration is currently analyzing the first three years of data and anticipates releasing updated measurements of dark energy and the expansion history of the Universe in the coming year. The expanded results released today align with earlier findings from DESI, favoring an evolving dark energy model, raising anticipation for the upcoming analysis.

“Dark matter constitutes about a quarter of the Universe, and dark energy makes up another 70 percent, yet we still don’t fully understand either,” said Mark Maus, a PhD student at Berkeley Lab and UC Berkeley, who worked on theory and validation modeling for the new analysis. “The fact that we can capture images of the Universe to address these monumental questions is truly remarkable.”

While DESI’s year-one data is not yet publicly available, researchers can access the early data release. These files are available via the DESI collaboration and as searchable databases of catalogs and spectra through the Astro Data Lab and SPARCL at the Community Science and Data Center, a program of NSF NOIRLab.