Researchers see hints that dark energy, widely thought to be a "cosmological constant," might be evolving over time in unexpected ways.
New results from the Dark Energy Spectroscopic Instrument (DESI) collaboration, one of the most extensive surveys of the cosmos ever conducted, reveal that the impact of dark energy may be weakening over time - and the standard model of how the universe works may need an update.
This recent finding uses data from the first three years of observations and includes nearly 15 million galaxies and quasars, more than doubling the dataset used in DESI's first analysis, which was presented less than one year ago. It's a major leap forward, improving the experiment's precision with a dataset that is more than double what was used in DESI's first analysis which also hinted at an evolving dark energy.
"Our results are truly remarkable," said Klaus Honscheid, lead scientist of DESI instrument operations and a physics professor at The Ohio State University. "We are seeing even stronger evidence for a fundamental shift in how we think about dark energy."
DESI is an international experiment with more than 900 researchers from over 70 institutions around the world and is managed by the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab). Ohio State has been a core member of the DESI collaboration for over a decade and includes 12 researchers actively working on the collection and analysis of DESI data.
The collaboration shared their findings today in multiple papers that will be posted online and later in a presentation at the American Physical Society's Global Physics Summit in Anaheim, California.
Taken alone, DESI's data is consistent with our standard model of the universe. However, when paired with other measurements, there are mounting indications that the impact of dark energy may be weakening over time and other models may be a better fit. Those other measurements include the light left over from the dawn of the universe; supernovae, or exploding stars; and how light from distant galaxies is warped by gravity.
"These measurements show some evidence that the standard model of cosmology is not the best explanation," said Ashley Ross, lead scientist for the DESI large-scale structure catalogs and a research professor of physics at Ohio State. "We now have multiple datasets that are pointing in this direction, which strengthens our confidence in our results."
While DESI's previous release initially showed a preference for dynamical dark energy, many researchers thought a statistical fluke was a more likely explanation than a major discovery, said Paul Martini, one of the coordinators of the current analysis and a professor of astronomy at Ohio State. "Yet the evidence for dynamical dark energy has gotten stronger with more data, and it has passed new and tougher tests, so we are more confident and more excited."
In parallel to the DESI analysis, work is going on to plan the next phases of DESI that will follow at the end of the decade as well as for even more powerful instruments that will be built in the future. Besides DESI, other experiments coming online over the next several years will also provide complementary datasets for future analyses.
The DESI collaboration also recently announced that its Data Release 1 (DR1) is now available for anyone to explore. With information on millions of celestial objects, the dataset will support a wide range of astrophysical research by others, in addition to DESI's cosmology goals.
The discovery of dark energy, nearly 30 years ago, was already the biggest surprise of my scientific lifetime," said David Weinberg, a professor of astronomy at Ohio State who also contributed to the DESI analysis. "These new measurements offer the strongest evidence so far that dark energy evolves, which would be another mind-blowing change to our understanding of how the universe works."
DESI is supported by the DOE Office of Science and by the National Energy Research Scientific Computing Center, a DOE Office of Science national 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.
Other Ohio State members of the collaboration include Mikel Charles, Xinyi Chen, Meagan Herbold, Naim Karacayli, Peter Taylor, Wynne Turner, Molly Wolfson and Erik Zaborowski. 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.
