Free Astronomy Magazine January-February 2025

50 JANUARY-FEBRUARY 2025 ASTRO PUBLISHING T he Dark Energy Spectroscopic Instrument (DESI) making observations in the night sky on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory in Arizona. [KPNO/NOIRLab/NSF/AURA/T. Slovinský] celerating expansion of our Uni- verse that is typically attributed to dark energy. The DESI collaboration shared their results in several papers. The com- plex analysis used nearly six million galaxies and quasars and lets re- searchers see up to 11 billion years into the past. With just one year of data, DESI has made the most pre- cise overall measurement of the growth of cosmic structure, surpass- ing previous efforts that took decades to complete. Today’s results provide an extended analysis of DESI’s first year of data, which made the largest 3D map of our Universe to date and revealed hints that dark energy might be evolving over time. The results looked at a particular feature of how galaxies cluster known as baryon acoustic oscillations (BAO). The new analysis broadens the scope by measuring how galaxies and matter are distributed on dif- ferent scales throughout space. The study also provided improved con- straints on the mass of neutrinos, the only fundamental particles whose masses have not yet been precisely measured. Neutrinos influ- ence the clustering pattern of galax- ies very slightly but this can be measured with the quality of the DESI data. The DESI constraints are the most stringent to date, comple- menting constraints from laboratory measurements. The study required months of addi- tional work and cross-checks. As be- fore, it used a technique to hide the result from the scientists until the end, mitigating any unconscious bias. “This research is part of one of the key projects of the DESI experiment — to learn about the fundamental aspects of our Universe at large scales, such as matter dis- tribution and the behav- ior of dark energy, as well as fundamental as- pects of particles,” says Stephanie Juneau, NSF NOIRLab astronomer and a member of the DESI collaboration. “By com- paring the evolution of the matter distribution in the Universe with exist- ing predictions, including Einstein’s theory of general relativ- ity and competing theories, we’re really tightening the possibilities on our models of gravity.” The collaboration is currently ana- lyzing the first three years of col- lected data and expects to present updated measurements of dark en- ergy and the expansion history of our Universe in 2025. DESI’s ex- panded results are consistent with the experiment’s earlier preference for an evolving dark energy, adding to the anticipation of the upcoming analysis. “Dark matter makes up about a quarter of the Universe, and dark energy makes up another 70 per- cent, and we don’t really know what either one is,” said Mark Maus, a PhD student at Berkeley Lab and UC Berkeley who worked on theory and validation modeling pipelines for the new analysis. “The idea that we can take pictures of the Universe and tackle these big, fundamental questions is mind-blowing.” I n this 360-degree video, take an interactive flight through millions of galaxies mapped using coor- dinate data from DESI. [Fiske Planetarium/CU Boul- der/DESI collaboration] !