Subtle but intriguing deviations from the simplest picture of dark energy

An artistic celebration of the Dark Energy Spectroscopic Instrument (DESI) year-one data, showing a slice of the larger 3D map that DESI is constructing during its five-year survey. By mapping objects across multiple periods of cosmic history with extremely high precision, DESI is allowing astronomers to make unprecedented measurements of dark energy and its effect on the accelerating expansion of the Universe. DESI’s map reveals the large-scale structure of the Universe, showing clumps of galaxies separated by voids where there are fewer objects. This pattern is a result of large pressure waves that permeated the early Universe and is reflected in the cosmic microwave background — a 2D snapshot of the radiation that filled the Universe shortly after the Big Bang-- and leave this imprint on the 3D galaxy distribution in the late Universe. DESI is mounted on the U.S. National Science Foundation Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory, a Program of NSF NOIRLab. This version of the DESI map includes 600,000 galaxies — less than 0.1% of the survey's full volume. The locations of objects in the data slice do not correlate with their locations on-sky shown in this image. ( credits: CC BY 4.0 File: Artistic Composition of DESI Year-One Data Slice Above the Nicholas U Mayall 4-meter Telescope)

An annotation of DESI's contour plot. The plot describes the “behavior” of dark energy – how its density changes as space expands. Credit: Claire Lamman/DESI collaboration