New DESI data shed light on gravity's pull in the universe

DESI observes the sky from the Mayall Telescope, shown here during the 2023 Geminid meteor shower. Credit: KPNO/NOIRLab/NSF/AURA/R. Sparks

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 the 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.

"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." 

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

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. 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.

These results provide an extended analysis of DESI's first year of data, which in April made the largest 3D map of the universe to date and revealed hints that dark energy might be evolving over time.

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 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. 

by Lawrence Berkeley National Laboratory

Source: New DESI data shed light on gravity's pull in the universe