EPFL scientists join DESI to reveal evolving dark energy
DESI observes the sky from the Mayall Telescope, shown here beneath the Milky Way. Credit: KPNO/NOIRLab/NSF/AURA/R.T. Sparks
EPFL’s astrophysicists have contributed to DESI’s 15-million-galaxy map, hinting at a shift in our understanding of dark energy.
New findings from the Dark Energy Spectroscopic Instrument (DESI) collaboration suggest that dark energy – the mysterious force driving the universe’s accelerating expansion – may be evolving over time. The results, based on the largest 3D map of the cosmos ever constructed, were unveiled today in a series of scientific papers and a presentation at the American Physical Society’s Global Physics Summit.
EPFL’s Laboratory of Astrophysics, led by Prof. Jean-Paul Kneib, played a key role in DESI’s data analysis. The team, which includes postdoctoral researchers Rafaela Gsponer and Antoine Rocher, as well as several PhD students, contributed to refining the clustering measurements of galaxies and quasars, critical for enhancing the accuracy of the baryon acoustic oscillation (BAO) signal.
The BAO signal is fundamental for measuring the expansion history of the Universe and the evolving influence of dark energy over cosmic time. “Working within DESI as an early career scientist is an incredible opportunity,” says Rafaela Gsponer. “The scale and precision of these BAO measurements are unprecedented, and it’s inspiring to contribute to a global effort that could reshape our understanding of dark energy.” The team at EPFL was strongly involved in stating the accuracy of the measurements.
“What we are seeing is deeply intriguing,” says Alexie Leauthaud-Harnett, co-spokesperson for DESI and a professor at UC Santa Cruz. “It is exciting to think that we may be on the cusp of a major discovery about dark energy and the fundamental nature of our universe.”
DESI’s latest data spans nearly 15 million galaxies and quasars observed over three years, creating a map that traces the influence of dark energy over the past 11 billion years. While the data alone fits within the standard Lambda Cold Dark Matter (Lambda CDM) cosmological model, its combination with other experiments – including studies of the cosmic microwave background (CMB), supernovae, and weak gravitational lensing – points toward a intriguing possibility: dark energy might not be constant, but evolving.
“It’s looking more and more like we may need to modify our standard model of cosmology to make these different datasets make sense together – and evolving dark energy seems promising,” says Will Percival, DESI co-spokesperson.
The statistical significance of this finding has yet to meet the 5-sigma threshold required for a formal discovery, but the current range of 2.8 to 4.2 sigma already has scientists taking notice.
DESI is mounted on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory in Arizona, USA. The experiment is operated by an international collaboration of over 900 researchers across more than 70 institutions. EPFL is one of the major European partners.
The DESI collaboration will continue gathering data, aiming to map a total of 50 million galaxies and quasars by the survey’s completion. Meanwhile, EPFL’s Laboratory of Astrophysics will remain deeply involved in the analysis of this treasure trove of cosmological information.
“It is exciting to have new state-of -the-art datasets to study the cosmological standard model, especially with this exciting finding we have at the moment,” says Antoine Rocher. This latest achievement builds on EPFL’s longstanding involvement with DESI, as previously highlighted when researchers unveiled the largest 3D map of the universe.
Berkeley Lab’s official release and supporting materials, including images and videos, are available here.
The DESI project is supported by the U.S. Department of Energy Office of Science, the U.S. National Science Foundation, and numerous international partners, including EPFL.